user16545: Metta sutra says "May all living beings be happy minded." This seems illogical to me as all living beings cannot be happy minded at a particular moment of time. I also feel that contemplating on anything that is false will not lead me to the ultimate truth. In my view loving kindness should be better cultivated by knowing the true nature of things because if we get insight into real nature of things then we will automatically develop kindness by clearly seeing dukkha and we would be able to understand the suffering of others in a better way. Note: I do not intend to offend great Buddhist scriptures. I asked this question to clear my ignorance.

user13709: There are many suttas that discuss mettāsahagatena. Let's look at a quote from one of these, SN46.54:

‘Come, mendicants, give up these five hindrances, corruptions of the heart that weaken wisdom, and meditate spreading a heart full of love to one direction, and to the second, and to the third, and to the fourth. In the same way above, below, across, everywhere, all around, spread a heart full of love to the whole world—abundant, expansive, limitless, free of enmity and ill will.

Here the translation states "spread a heart full of love to the whole world". This is similar to "May all living being be happy-minded." Yet it is subtly different. The difference is the emphasis of living with an open heart absent ill-will. We start with ourselves and wish that others, all others, come to this understanding of metta as well. 
It is easy to wish that loved ones be happy-minded. Yet that would be limited. Notice that the sutta clearly mentions "the whole world." And the world includes people who kill, lie, cheat, steal, etc. How could we wish them happiness? It seems illogical. 
And yet, if one gives up killing, lying, cheating, stealing, etc., there is less suffering. Therefore, surely we should wish an end of suffering to the whole world. That would be logical. 
The difficulty with the translation "happy-minded" is that it could be understood in several ways, some of which are completely illogical (i.e., should we smile all the time to show we are happy?). However, "happy-minded" can also be understood to mean "inclined towards happiness for all".  Indeed, it is logical that suffering would be less if we were all inclined towards happiness for all. 
And to be always inclined towards happiness for all, we would have to relinquish dukkha (greed, hate and delusion). In particular, we would have to relinquish identity view.

user8157: The Metta Sutta says:

Sukhino va khemino hontu, Sabbasattā bhavantu sukhitattā.
Wishing: In gladness and in safety, May all beings be at ease
In safety and in bliss, May creatures all be of a blissful heart.
May all be well and secure, May all beings be happy!
May all beings be happy and safe. May they have happy minds.
Think: Happy, at rest, may all beings be happy at heart.
May beings all live happily and safe, and may their hearts rejoice
  within themselves.

I think the above practise of metta is not a magical unrealistic expectation that others be happy but is the practise of you personally acting when interacting with others to put others at ease, such as, for example, to be friendly towards them, to honor them, to make them feel good via your own radiating of love towards them, to not criticize them, to not feel ill-will or judgment towards them (which they may sense), to have unconditional love towards them, to not rebuke them for their wrong heretical puthujjana views about Buddhism, to not call them & not treat them as 'puthujjana', etc. 

If, mendicants, a mendicant cultivates a mind of love (mettācittaṃ)
  even as long as a finger snap, they’re called a mendicant who does not
  lack absorption, who follows the Teacher’s instructions, who responds
  to advice, and who does not eat the country’s alms in vain. How much
  more so those who make much of it!”
AN 1.53


user-1: That is, on a more focused view, right, householder Sriram Goutam P, and no offend of the Buddhas teachings at all but a wise observed encouragement.
- Namo tassa bhagavato arahato sammā-sambuddhassa -
While the development of metta certainly has not the purpose to change the world of others, or give oneself the task to feel such as love toward any being, it's used to develop an attitude of goodness and goodwill toward all, what ever might be the quality of relation. See "Mettā means Goodwill", which corrects certain wrong transmitted attributes of metta.
Giving others the wish "May these beings be free from animosity, free from oppression, free from trouble, and may they look after themselves with ease!"
Mostly such a honest wish, acting without harm, is all one could do for others and having done all what one can do gives release, freedom of debts.
There are less who actually do not give such a gift, also in action, but mostly only toward those regarded as own or regarded a heading after ones aims and desires.
Once the ensnared net of battle each other can be seen, that there is no real justification why siding snake or mouse, and that beings are heirs of their actions, i.e. right view arises, metta, the wish for the best for all can non-hypocritical developted toward all in the universe, good, wise and fools, gifted or worse. That is one huge different to the metta development of the Jains:

They get their disciple to undertake the following practice: 'Here, my good man. Lay down the rod with regard to beings who live more than 100 leagues to the east... more than 100 leagues to the west... more than 100 leagues to the north... more than 100 leagues to the south.' Thus they get the disciple to undertake kindness & sympathy to some beings, but not to others.
"On the Uposatha day, they get their disciple to undertake the following practice: 'Here, my good man. Having stripped off all your clothing, say this: "I am nothing by anything or of anything. Thus there is nothing by anything or of anything that is mine."' 
Thus at a time when he should be persuaded to undertake truthfulness, he is persuaded to undertake falsehood. At the end of the night, he resumes the consumption of his belongings, even though they aren't given back to him. This counts as stealing, I tell you. Such is the Uposatha of the Jains, Visakha. When this Uposatha of the Jains is undertaken, it is not of great fruit or great benefit, not of great glory or great radiance.

And there is the strategical giving of metta of the cowherd, trading with something which is not their own to walk on.
So right view, at least in faith, is the prerequistite for developing metta that leads into the Brahma realms or even beyond:
right view (4 Noble truth) > right resolve (=metta) > right virtue! > right meditation (development) > release
And if investigating the Karaṇīya Metta-Sutta one finds that in the starting verses.

He who is skilful in his welfare,
  And wishes to attain that state of Peace (e.g. at least a firm faith-follower, instructed, and after Nibbana)
  Should act thus:...

Further, there is not really any evidence that such as metta-bhavana was taught much toward people of wrong view.

"Now, Kalamas, one who is a disciple of the noble ones — thus devoid of greed, devoid of ill will, undeluded, alert, & resolute — keeps pervading the first direction [the east] — as well as the second direction, the third, & the fourth — with an awareness imbued with good will. Thus he keeps pervading above, below, & all around, everywhere & in every respect the all-encompassing cosmos with an awareness imbued with good will: abundant, expansive, immeasurable, free from hostility, free from ill will.

And at least, metta is deply connected with even conventional right view, not to speak that "maha-metta" is an application of Noble Ones.

"And how is one made pure in three ways by mental action? There is the case where a certain person is not covetous. He does not covet the belongings of others, thinking, 'O, that what belongs to others would be mine!' He bears no ill will and is not corrupt in the resolves of his heart. [He thinks,] 'May these beings be free from animosity, free from oppression, free from trouble, and may they look after themselves with ease!' He has right view and is not warped in the way he sees things: 'There is what is given, what is offered, what is sacrificed. There are fruits & results of good & bad actions. There is this world & the next world. There is mother & father. There are spontaneously reborn beings; there are brahmans & contemplatives who, faring rightly & practicing rightly, proclaim this world & the next after having directly known & realized it for themselves.' This is how one is made pure in three ways by mental action."
— AN 10.176

There is a generouse and very useful essay on metta by Ven. Ñāṇadassana as gift of Dhamma: Karaṇīya Metta-Sutta, including also detail explainings of the prerequisites of metta-development as means for higher and beyond.
The generous essay Metta Means Goodwill helps to get ride of certain popular missunderstandings.
There have been related answers on the topic before and maybe my person can add them here later:

Some words on blessings
How to view people with metta and karuna?

Best wishes that householder soon arrives at right metta, right view and/or pushes if further till highest liberation.

...And not holding to [wrong] view,
  Being virtuous, endowed with right vision,
  And discarding desire for sensual pleasures,
  One surely never again will be reborn
  in a womb.

A possible extended Answer, as well as given space for discussion and deriving questions, can be accessed here: [Q&A] How does metta sutra, how is metta, loving kindness, develop?
(Note that this Dhamma gift is not given for trade, exchange, stacks, entertainments to bind or conduct demerits with it, but for release from this wheel)

user471: When you understand the suffering of others, this would result in you developing your compassion (karuna) and not exactly loving kindness (metta). So, compassion is a bit different. Compassion is how one deals with others' suffering (dukkha) while renunciation is how one deals with one's own suffering. Of course, there may be some overlap between the two.
Then what about loving kindness (metta)? This term metta has also been translated as benevolence, friendliness, amity, good will and universal love.
You're perfectly right that all beings cannot be happy-minded at once.
Cultivating metta is about changing YOUR state of mind, and not actually changing other people's state of mind.
Loving kindness is about you changing your thoughts, emotions, intentions, attitude, outlook and conduct, in such a way that it radiates with benevolence and friendliness to all beings (including yourself). It is so that you become the true friend who wishes everyone, without discrimination, to be happy and at ease with themselves. Loving kindness is a cure for one's ill will towards others.
On the other hand, compassion is about you trying to understand the suffering of others and trying to alleviate the suffering of others, or at least not make it worse. Compassion is a cure for one's contempt for others.

16545: <p>Metta sutra says "May all living beings be happy minded." This seems illogical to me as all living beings cannot be happy minded at a particular moment of time. I also feel that contemplating on anything that is false will not lead me to the ultimate truth. In my view loving kindness should be better cultivated by knowing the true nature of things because if we get insight into real nature of things then we will automatically develop kindness by clearly seeing dukkha and we would be able to understand the suffering of others in a better way. Note: I do not intend to offend great Buddhist scriptures. I asked this question to clear my ignorance.</p>
 13709: <p>There are many suttas that discuss <a href="https://voice.suttacentral.net/scv/index.html?r=0.9646125710050402#/sutta?iVoice=0&amp;ips=6&amp;lang=en&amp;maxResults=50&amp;search=mett%C4%81sahagatena&amp;showId=false&amp;showLang=0" rel="nofollow noreferrer">mettāsahagatena</a>. Let's look at a quote from one of these, <a href="https://suttacentral.net/sn46.54/en/sujato" rel="nofollow noreferrer">SN46.54</a>:</p>

<blockquote>
  <p>‘Come, mendicants, give up these five hindrances, corruptions of the heart that weaken wisdom, and meditate spreading a heart full of love to one direction, and to the second, and to the third, and to the fourth. In the same way above, below, across, everywhere, all around, spread a heart full of love to the whole world—abundant, expansive, limitless, free of enmity and ill will.</p>
</blockquote>

<p>Here the translation states "spread a heart full of love to the whole world". This is similar to "May all living being be happy-minded." Yet it is subtly different. The difference is the emphasis of living with an open heart absent ill-will. We start with ourselves and wish that others, all others, come to this understanding of metta as well. </p>

<p>It is easy to wish that loved ones be happy-minded. Yet that would be limited. Notice that the sutta clearly mentions "the whole world." And the world includes people who kill, lie, cheat, steal, etc. How could we wish them happiness? It seems illogical. </p>

<p>And yet, if one gives up killing, lying, cheating, stealing, etc., there is less suffering. Therefore, surely we should wish an end of suffering to the whole world. That would be logical. </p>

<p>The difficulty with the translation "happy-minded" is that it could be understood in several ways, some of which are completely illogical (i.e., should we smile all the time to show we are happy?). However, "happy-minded" can also be understood to mean "inclined towards happiness for all".  Indeed, it is logical that suffering would be less if we were all inclined towards happiness for all. </p>

<p>And to be always inclined towards happiness for all, we would have to relinquish dukkha (greed, hate and delusion). In particular, we would have to relinquish identity view.</p>
 8157: <p>The Metta Sutta says:</p>

<blockquote>
  <p>Sukhino va khemino hontu, Sabbasattā bhavantu sukhitattā.</p>
  
  <p>Wishing: In gladness and in safety, May all beings be at ease</p>
  
  <p>In safety and in bliss, May creatures all be of a blissful heart.</p>
  
  <p>May all be well and secure, May all beings be happy!</p>
  
  <p>May all beings be happy and safe. May they have happy minds.</p>
  
  <p>Think: Happy, at rest, may all beings be happy at heart.</p>
  
  <p>May beings all live happily and safe, and may their hearts rejoice
  within themselves.</p>
</blockquote>

<p>I think the above practise of metta is not a magical unrealistic expectation that others be happy but is the practise of you personally acting when interacting with others to put others at ease, such as, for example, to be friendly towards them, to honor them, to make them feel good via your own radiating of love towards them, to not criticize them, to not feel ill-will or judgment towards them (which they may sense), to have unconditional love towards them, to not rebuke them for their wrong heretical <em>puthujjana</em> views about Buddhism, to not call them &amp; not treat them as '<a href="http://www.palikanon.com/english/wtb/n_r/puthujjana.htm" rel="nofollow noreferrer"><em>puthujjana</em></a>', etc. </p>

<blockquote>
  <p>If, mendicants, a mendicant cultivates a mind of love (mettācittaṃ)
  even as long as a finger snap, they’re called a mendicant who does not
  lack absorption, who follows the Teacher’s instructions, who responds
  to advice, and who does not eat the country’s alms in vain. How much
  more so those who make much of it!”</p>
  
  <p>AN 1.53</p>
</blockquote>
 -1: <p>That is, on a more focused view, right, householder Sriram Goutam P, and no offend of the Buddhas teachings at all but a wise observed encouragement.</p>

<p><a href="http://zugangzureinsicht.org/html/tipitaka/an/an03/an03.070.than_en.html" rel="nofollow noreferrer">- Namo tassa bhagavato arahato sammā-sambuddhassa -</a></p>

<p>While the development of metta certainly has not the purpose to change the world of others, or give oneself the task to feel such as love toward any being, it's used to develop an attitude of goodness and goodwill toward all, what ever might be the quality of relation. See "<a href="http://zugangzureinsicht.org/html/lib/authors/thanissaro/beyond_en.html#ch4" rel="nofollow noreferrer">Mettā means Goodwill</a>", which corrects certain wrong transmitted attributes of metta.</p>

<p>Giving others the wish <code>"May these beings be free from animosity, free from oppression, free from trouble, and may they look after themselves with ease!"</code></p>

<p>Mostly such a honest wish, acting without harm, is all one could do for others and having done all what one can do gives release, freedom of debts.</p>

<p>There are less who actually do not give such a gift, also in action, but mostly only toward those regarded as own or regarded a heading after ones aims and desires.</p>

<p>Once the ensnared net of battle each other can be seen, that there is no real justification why siding snake or mouse, and that beings are heirs of their actions, i.e. right view arises, metta, the wish for the best for all can non-hypocritical developted toward all in the universe, good, wise and fools, gifted or worse. That is one huge different to the metta <a href="http://zugangzureinsicht.org/html/tipitaka/an/an03/an03.070.than_en.html" rel="nofollow noreferrer">development of the Jains</a>:</p>

<blockquote>
  <p>They get their disciple to undertake the following practice: 'Here, my good man. Lay down the rod with regard to beings who live more than 100 leagues to the east... more than 100 leagues to the west... more than 100 leagues to the north... more than 100 leagues to the south.' Thus they get the disciple to undertake kindness &amp; sympathy to some beings, but not to others.</p>
  
  <p>"On the Uposatha day, they get their disciple to undertake the following practice: 'Here, my good man. Having stripped off all your clothing, say this: "I am nothing by anything or of anything. Thus there is nothing by anything or of anything that is mine."' </p>
  
  <p>Thus at a time when he should be persuaded to undertake truthfulness, he is persuaded to undertake falsehood. At the end of the night, he resumes the consumption of his belongings, even though they aren't given back to him. This counts as stealing, I tell you. Such is the Uposatha of the Jains, Visakha. When this Uposatha of the Jains is undertaken, it is not of great fruit or great benefit, not of great glory or great radiance.</p>
</blockquote>

<p>And there is the strategical giving of metta of the cowherd, trading with something which is not their own to walk on.</p>

<p>So right view, at least in faith, is the prerequistite for developing metta that leads into the Brahma realms or even beyond:</p>

<p><code>right view (4 Noble truth) &gt; right resolve (=metta) &gt; right virtue! &gt; right meditation (development) &gt; release</code></p>

<p>And if investigating the Karaṇīya Metta-Sutta one finds that in the starting verses.</p>

<blockquote>
  <p>He who is skilful in his welfare,
  And wishes to attain that state of Peace (e.g. at least a firm faith-follower, instructed, and after Nibbana)
  Should act thus:...</p>
</blockquote>

<p>Further, there is not really any evidence that such as metta-bhavana was taught much toward people of wrong view.</p>

<blockquote>
  <p>"Now, <a href="http://zugangzureinsicht.org/html/tipitaka/an/an03/an03.065.than_en.html" rel="nofollow noreferrer">Kalamas</a>, <strong>one who is a disciple of the noble ones — thus devoid of greed, devoid of ill will, undeluded, alert, &amp; resolute</strong> — keeps pervading the first direction [the east] — as well as the second direction, the third, &amp; the fourth — with an awareness imbued with good will. Thus he keeps pervading above, below, &amp; all around, everywhere &amp; in every respect the all-encompassing cosmos with an awareness imbued with good will: abundant, expansive, immeasurable, free from hostility, free from ill will.</p>
</blockquote>

<p>And at least, metta is deply connected with even conventional right view, not to speak that "maha-metta" is an application of Noble Ones.</p>

<blockquote>
  <p>"And how is one made pure in three ways by mental action? There is the case where a certain person is not covetous. He does not covet the belongings of others, thinking, 'O, that what belongs to others would be mine!' He bears no ill will and is not corrupt in the resolves of his heart. [He thinks,] '<strong>May these beings be free from animosity, free from oppression, free from trouble, and may they look after themselves with ease!</strong>' <strong>He has <a href="http://zugangzureinsicht.org/html/ptf/dhamma/sacca/sacca4/samma-ditthi/index_en.html" rel="nofollow noreferrer">right view</a></strong> and is not warped in the way he sees things: 'There is what is given, what is offered, what is sacrificed. There are fruits &amp; results of good &amp; bad actions. There is this world &amp; the next world. There is mother &amp; father. There are spontaneously reborn beings; there are brahmans &amp; contemplatives who, faring rightly &amp; practicing rightly, proclaim this world &amp; the next after having directly known &amp; realized it for themselves.' This is how one is made pure in three ways by mental action."</p>
  
  <p>— <a href="http://zugangzureinsicht.org/html/tipitaka/an/an10/an10.176.than_en.html#mind" rel="nofollow noreferrer">AN 10.176</a></p>
</blockquote>

<p>There is a generouse and very useful essay on metta by Ven. Ñāṇadassana as gift of Dhamma: <strong><a href="http://zugangzureinsicht.org/html/lib/authors/nanadassana/metta_en.html" rel="nofollow noreferrer">Karaṇīya Metta-Sutta</a></strong>, including also detail explainings of the prerequisites of metta-development as means for higher and beyond.</p>

<p>The generous essay <a href="http://zugangzureinsicht.org/html/lib/authors/thanissaro/beyond_en.html#ch4" rel="nofollow noreferrer">Metta Means Goodwill</a> helps to get ride of certain popular missunderstandings.</p>

<p>There have been related answers on the topic before and maybe my person can add them here later:</p>

<ul>
<li><p><a href="https://buddhism.stackexchange.com/a/33650/11235">Some words on blessings</a></p></li>
<li><p><a href="http://sangham.net/index.php/topic,8350.msg13700/topicseen.html#msg13700" rel="nofollow noreferrer">How to view people with metta and karuna?</a></p></li>
</ul>

<p>Best wishes that householder soon arrives at right metta, right view and/or pushes if further till highest liberation.</p>

<blockquote>
  <p>...And not holding to [wrong] view,
  Being virtuous, endowed with right vision,
  And discarding desire for sensual pleasures,
  One surely never again will be reborn
  in a womb.</p>
</blockquote>

<p>A possible extended Answer, as well as given space for discussion and deriving questions, can be accessed here: <a href="http://sangham.net/index.php/topic,9336.msg19116.html#msg19116" rel="nofollow noreferrer">[Q&amp;A] How does metta sutra, how is metta, loving kindness, develop?</a></p>

<p><em>(Note that this Dhamma gift is not given for trade, exchange, stacks, entertainments to bind or conduct demerits with it, but for release from this wheel)</em></p>
 471: <p>When you understand the suffering of others, this would result in you developing your compassion (<em>karuna</em>) and not exactly loving kindness (<em>metta</em>). So, compassion is a bit different. Compassion is how one deals with others' suffering (<em>dukkha</em>) while renunciation is how one deals with one's own suffering. Of course, there may be some overlap between the two.</p>

<p>Then what about loving kindness (<em>metta</em>)? This term <em>metta</em> has also been translated as benevolence, friendliness, amity, good will and universal love.</p>

<p>You're perfectly right that all beings cannot be happy-minded at once.</p>

<p>Cultivating <em>metta</em> is about changing YOUR state of mind, and not actually changing other people's state of mind.</p>

<p>Loving kindness is about you changing your thoughts, emotions, intentions, attitude, outlook and conduct, in such a way that it radiates with benevolence and friendliness to all beings (including yourself). It is so that you become the true friend who wishes everyone, without discrimination, to be happy and at ease with themselves. Loving kindness is a cure for one's ill will towards others.</p>

<p>On the other hand, compassion is about you trying to understand the suffering of others and trying to alleviate the suffering of others, or at least not make it worse. Compassion is a cure for one's contempt for others.</p>
