user13525: It seems to me that there is a popular and strong belief that if you reach enlightenment, and thus have four immeasurables, you can help a person without making them feel extra suffering or fighting back. This can be illustrated by the sutta Aṅgulimāla. The Buddha can stop him easily and effortlessly. The premise here is that enlightenment = perfect knowledge, and/or four immeasurables = you and the others are truly the same, so that you can understand that person inside out.
The equal sign = is more like implies that rather exactly means.
However, realistically, I think this is impossible. There are situations that achieving enlightenment does not mean perfect knowledge. For example, you can reach enlightenment in a radioactive region. This is not loving-kindness yourself. Likewise, one can never claim to perfectly understand the inner state of the other person, especially without face-to-face conversation. What it seems to be true is that enlightenment = having no distortion, and/or four immeasurables = being able to vision a way to help the others getting out of their suffering.
Perhaps this is just a matter of defining what enlightenment is. This is fine. But in this case, its necessary consequence is that no human can achieve this state (though can absolutely achieve mindfulness or practice eightfold path).
Is this correct?

user2282: 
This can be illustrated by the sutta Aṅgulimāla. The Buddha can stop him easily.

If by perfect knowledge, you meant the Iddhis, then while it Can be developed once one's attained enlightenment, but it's not a Necessary condition. For sutta support, see SN 12.70. Also see the discussion about different types of enlightened disciples in AN 4.87

user254: One of the things that's special about the Budda, specifically, compared with other enlightened people, is that the Buddha is especially good at teaching others -- for example:

How the Buddha is distinguished from other arahants
Now all these epithets are true for the Buddha as well, but the Buddha is not described in this way; for these terms emphasize the attainment of one's own liberation, and the Buddha is extolled, not primarily as the one who has attained his own liberation, but as the one who opens the doors of liberation for others. That is, even in the archaic suttas of the Nikāyas, an "other-regarding" significance is already being subtly ascribed to the Buddha's status that is not ascribed to the arahant.

See also Pratyekabuddha:

According to the Theravada school, paccekabuddhas ("one who has attained to supreme and perfect insight, but who dies without proclaiming the truth to the world") are unable to teach the Dhamma, which requires the omniscience and supreme compassion of a sammāsambuddha, and even he hesitates to attempt to teach. Paccekabuddhas give moral teachings but do not bring others to enlightenment. They leave no sangha as a legacy to carry on the Dhamma.

I think that all arahants have a certain amount of knowledge or insight -- e.g. about the nature of suffering and the dhamma.
Some people, including the Buddha, and not all of them enlightened, also have "psychic powers" -- the ability to know what other people are thinking, what their mind-state is. The Buddha used this power to help him teach people who were ready, when they were ready.

user19257: Yes. Fully enlightened person has the perfect knowledge.
If you explore the reasons behind the knowledge gathering, eventually you will boil them down to a single reason. That is the “self interest”. And then the question comes to who or what is self? 
The whole purpose of Buddhism is to discover this “self” or “me”.
Eventually you will discover that the “self” is just a delusion.
Then you will become an enlightened person.

user14789: In buddhism, Enlightenment is the "direct knowledge" about suffering, the origin, the cessation https://www.accesstoinsight.org/tipitaka/sn/sn56/sn56.011.than.html
the four immeasurables  is just how to get to Brahma world, like here https://suttacentral.net/mn99/en/sujato  so it is not Enlightenment. When you claim that the four immeasurables  is Enlightenment you are a hindu and that's totally wrong in buddhism.
So you are mixing hinduism and buddhism. In hinduism the path to nibanna is to generate merits over and over, same thing with the jains. They have to burn up past bad karma and create lots of good karma..
But that's very wrong view.
In buddhism generating merit is useless to get enlightened. Merit gets you a good birth and that's all. In buddhism you need to know about suffering, the origin, the cessation and the path to the cessation of suffering.
So do not confuse the path of merit, the path of Enlightenment and Enlightenment itself.

13525: <p>It seems to me that there is a popular and strong belief that if you reach enlightenment, and thus have <a href="https://en.wikipedia.org/wiki/Brahmavihara" rel="nofollow noreferrer" title="Brahmavihara - Wikipedia">four immeasurables</a>, you can help a person without making them feel extra suffering or fighting back. This can be illustrated by the sutta <a href="https://en.wikipedia.org/wiki/A%E1%B9%85gulim%C4%81la" rel="nofollow noreferrer" title="Aṅgulimāla - Wikipedia">Aṅgulimāla</a>. The Buddha can stop him easily and effortlessly. The premise here is that <code>enlightenment = perfect knowledge</code>, and/or <code>four immeasurables = you and the others are truly the same, so that you can understand that person inside out</code>.</p>

<p><sub>The equal sign <code>=</code> is more like <code>implies that</code> rather <code>exactly means</code>.</sub></p>

<p>However, realistically, I think this is impossible. There are situations that achieving enlightenment does not mean perfect knowledge. For example, you can reach enlightenment in a radioactive region. This is not loving-kindness yourself. Likewise, one can never claim to perfectly understand the inner state of the other person, especially without face-to-face conversation. What it seems to be true is that <code>enlightenment = having no distortion</code>, and/or <code>four immeasurables = being able to vision a way to help the others getting out of their suffering</code>.</p>

<p>Perhaps this is just a matter of defining what <code>enlightenment</code> is. This is fine. But in this case, its necessary consequence is that no human can achieve this state (though can absolutely achieve <a href="https://en.wikipedia.org/wiki/Mindfulness" rel="nofollow noreferrer" title="Mindfulness - Wikipedia">mindfulness</a> or practice eightfold path).</p>

<p>Is this correct?</p>
 2282: <blockquote>
  <p>This can be illustrated by the sutta Aṅgulimāla. The Buddha can stop him easily.</p>
</blockquote>

<p>If by perfect knowledge, you meant the <a href="https://en.wikipedia.org/wiki/%E1%B9%9Addhi" rel="nofollow noreferrer">Iddhis</a>, then while it Can be developed once one's attained enlightenment, but it's not a Necessary condition. For sutta support, see <a href="https://suttacentral.net/sn12.70/en/bodhi" rel="nofollow noreferrer">SN 12.70</a>. Also see the discussion about different types of enlightened disciples in <a href="https://suttacentral.net/an4.87/en/sujato" rel="nofollow noreferrer">AN 4.87</a></p>
 254: <p>One of the things that's special about the Budda, specifically, compared with other enlightened people, is that the Buddha is especially good at teaching others -- <a href="https://www.accesstoinsight.org/lib/authors/bodhi/arahantsbodhisattvas.html" rel="nofollow noreferrer">for example</a>:</p>
<blockquote>
<p><strong>How the Buddha is distinguished from other arahants</strong></p>
<p>Now all these epithets are true for the Buddha as well, but the Buddha is not described in this way; for these terms emphasize the attainment of one's own liberation, and the Buddha is extolled, not primarily as the one who has attained his own liberation, but as the one who opens the doors of liberation for others. That is, even in the archaic suttas of the Nikāyas, an &quot;other-regarding&quot; significance is already being subtly ascribed to the Buddha's status that is not ascribed to the arahant.</p>
</blockquote>
<p>See also <a href="https://en.wikipedia.org/wiki/Pratyekabuddha" rel="nofollow noreferrer">Pratyekabuddha</a>:</p>
<blockquote>
<p>According to the Theravada school, paccekabuddhas (&quot;one who has attained to supreme and perfect insight, but who dies without proclaiming the truth to the world&quot;) are unable to teach the Dhamma, which requires the omniscience and supreme compassion of a sammāsambuddha, and even he hesitates to attempt to teach. Paccekabuddhas give moral teachings but do not bring others to enlightenment. They leave no sangha as a legacy to carry on the Dhamma.</p>
</blockquote>
<p>I think that all arahants have a certain amount of knowledge or insight -- e.g. about the nature of suffering and the dhamma.</p>
<p>Some people, including the Buddha, and not all of them enlightened, also have &quot;psychic powers&quot; -- the ability to know what other people are thinking, what their mind-state is. The Buddha used this power to help him teach people who were ready, when they were ready.</p>
 19257: <p>Yes. Fully enlightened person has the perfect knowledge.</p>

<p>If you explore the reasons behind the knowledge gathering, eventually you will boil them down to a single reason. That is the “self interest”. And then the question comes to who or what is self? </p>

<p>The whole purpose of Buddhism is to discover this “self” or “me”.</p>

<p>Eventually you will discover that the “self” is just a delusion.
Then you will become an enlightened person.</p>
 14789: <p>In buddhism, Enlightenment is the "direct knowledge" about suffering, the origin, the cessation <a href="https://www.accesstoinsight.org/tipitaka/sn/sn56/sn56.011.than.html" rel="nofollow noreferrer">https://www.accesstoinsight.org/tipitaka/sn/sn56/sn56.011.than.html</a></p>

<p>the four immeasurables  is just how to get to Brahma world, like here <a href="https://suttacentral.net/mn99/en/sujato" rel="nofollow noreferrer">https://suttacentral.net/mn99/en/sujato</a>  so it is not Enlightenment. When you claim that the four immeasurables  is Enlightenment you are a hindu and that's totally wrong in buddhism.</p>

<p>So you are mixing hinduism and buddhism. In hinduism the path to nibanna is to generate merits over and over, same thing with the jains. They have to burn up past bad karma and create lots of good karma..
But that's very wrong view.</p>

<p>In buddhism generating merit is useless to get enlightened. Merit gets you a good birth and that's all. In buddhism you need to know about suffering, the origin, the cessation and the path to the cessation of suffering.
So do not confuse the path of merit, the path of Enlightenment and Enlightenment itself.</p>
