user5444: According to the Buddhism's theory, one man's fate is destined by the past's karma.
Suppose that he faced an unfortunate incident at birth, which is due to past karma. Besides, his genes are inherited from his parents. In other words, his brain is also initiated by past karma. 
In this condition, all his ideas are also affected by the experience he has had, which is determined by past karma. To elaborate more, some are clever, some less, which can again be explained by karma.
But if the conventional human brain can be so strongly determined by the existence of karma, how can you say buddhism is not fatalism?

user21788: Strictly speaking Fate is described by the Greeks as being fixed and unchangeable.
Karma is changeable, mutable and immutable.
People use the word Fate to try to describe karma to people unfamiliar with Buddhism.

user254: This question might have been asked and answered well already, e.g. please read this answer.
Some reasons why 'belief in karma' is not 'fatalism' include:

'Fatalism' is often understood to mean "fate assigned to us by God", however Buddhist believe that "we are the author of our own karma"
Karma affects us, but it is not the only factor which affects us
Karma means, something like, 'an act of intention': our present intention affects our future (our future and present state is not pre-determined by fate, but is instead determined by our intentions)


To elaborate more, someone are clever, some less, which can be explained by the karma. But if the conventional human brain can be affected by the existence of karma, how can you say buddhism is not fatalism.

Whether intelligence is a result of birth (i.e. genes) or education (i.e. action) is a complicated subject (for example a book called The Blank Slate argued that it's the result of both).
For example, you can:

Intend to learn the first verse of the Dhammapada
As a result of having formed the intention, perform the actions which are necessary to achieve that (e.g. read the verse repeatedly until you have memorized it and can repeat it from memory)

In this example, because you had an intention, your brain was then affected: but it is not 'fatalism', instead it is you having an effect on your own brain as a result of your own choice.

user7141: The person who asked this question is wrong,as Buddhists we completely dump the theory "Karma is the last decider"
We believe in "Five niyamas"
Click this to learn "Five niyamas"
Karma is just a one variable in this not the final decider.
I guess this breaks the question and no further explaining is needed.Click the link given above and you will understand that Unlike many other beliefs Buddhism does not take away the right of free will because if it did there is no point of a Lord Buddha.
The very core of Buddhism is defying the tide and going against it with ones own free will and courage.So clearly Buddhism is not a fatalism because fate has no power over the will of a "One who is in the path".
Because no matter what he or she will reach nirvana and karma no matter how powerful it is can't change that.

user-1: Fatalism is the error of the ajivika sect of the Buddha's time, which the Buddha unequivocably rejected. That is how we can say that Buddhism is not fatalism. Logically, the reason is that even though our present is conditioned by the unfruited karma of our past, the effective principle of karma is volition or intention, which, being identical with reality (the Absolute), is fundamentally unconditioned and therefore free. The Absolute must be both ignorant and free, because it is (by definition) unconditioned. Primarily ignorant, once it becomes self-reflexive in samsara it becomes self-determining and therefore the cause of future unfruited karmas. This is also the proof of rebirth. Thus the Buddha stated that he knows the past and the present, but the future is indeterminate.

user5380: According to the Buddhism's theory, one man's fate is destined by the past's karma.
This is true that our conditions are determined by past karma, but they are determined by present as well.
A Brahman asked the Buddha in the Cula Kammavibhanga Sutta

Master Gotama, what is the reason, what is the condition, why inferiority and superiority are met with among human beings, among mankind? For one meets with short-lived and long-lived people, sick and healthy people, ugly and beautiful people, insignificant and influential people, poor and rich people, low-born and high-born people, stupid and wise people. What is the reason, what is the condition, why superiority and inferiority are met with among human beings, among mankind?

The Buddha replies by saying that our conditions are due to our past karma. This; however, is not fatalistic. The idea of karma revolves around the idea that we create our future. 
In the Devadaha Sutta the Buddha refutes two Jainism theories about karma 

The past determines present pleasure and pain, and the present determines future present and pain. 
The belief that you can do nothing in the present to get rid of suffering; all one could do is live with it. 

The Buddha rejected both of those theories that were taught in Jainism. Those two statements sound fatalistic.
The Buddha said that the past and present determine the present; thus, making it not fatalistic. 
Suffering, according to the Buddha, is due to past and present karma as well. 
There is no fatalism in Buddhism. 
The karma you mention in your question seems to be more of Jainist theories of karma than Buddhist theories of karma.

5444: <p>According to the Buddhism's theory, one man's fate is destined by the past's karma.
Suppose that he faced an unfortunate incident at birth, which is due to past karma. Besides, his genes are inherited from his parents. In other words, his brain is also initiated by past karma. </p>

<p>In this condition, all his ideas are also affected by the experience he has had, which is determined by past karma. To elaborate more, some are clever, some less, which can again be explained by karma.
But if the conventional human brain can be so strongly determined by the existence of karma, how can you say buddhism is not fatalism?</p>
 21788: <p>Strictly speaking Fate is described by the Greeks as being fixed and unchangeable.
Karma is changeable, mutable and immutable.</p>
<p>People use the word Fate to try to describe karma to people unfamiliar with Buddhism.</p>
 254: <p>This question might have been asked and answered well already, e.g. please read <a href="https://buddhism.stackexchange.com/a/9327/254">this answer</a>.</p>

<p>Some reasons why 'belief in karma' is not 'fatalism' include:</p>

<ul>
<li>'Fatalism' is often understood to mean "fate assigned to us by God", however Buddhist believe that "we are the author of our own karma"</li>
<li>Karma affects us, but it is not the only factor which affects us</li>
<li>Karma means, something like, 'an act of intention': our present intention affects our future (our future and present state is not pre-determined by fate, but is instead determined by our intentions)</li>
</ul>

<blockquote>
  <p>To elaborate more, someone are clever, some less, which can be explained by the karma. But if the conventional human brain can be affected by the existence of karma, how can you say buddhism is not fatalism.</p>
</blockquote>

<p>Whether intelligence is a result of birth (i.e. genes) or education (i.e. action) is a complicated subject (for example a book called <a href="https://en.wikipedia.org/wiki/The_Blank_Slate" rel="nofollow noreferrer">The Blank Slate</a> argued that it's the result of both).</p>

<p>For example, you can:</p>

<ul>
<li>Intend to learn <a href="http://www.tipitaka.net/tipitaka/dhp/verseload.php?verse=001" rel="nofollow noreferrer">the first verse of the Dhammapada</a></li>
<li>As a result of having formed the intention, perform the actions which are necessary to achieve that (e.g. read the verse repeatedly until you have memorized it and can repeat it from memory)</li>
</ul>

<p>In this example, because you had an intention, your brain was then affected: but it is not 'fatalism', instead it is you having an effect on your own brain as a result of your own choice.</p>
 7141: <p><strong>The person who asked this question is wrong,as Buddhists we completely dump the theory "Karma is the last decider"</strong></p>

<p>We believe in "Five niyamas"</p>

<p><a href="http://www.theravada.dk/?pageid=389" rel="nofollow"><strong>Click this to learn "Five niyamas"</strong></a></p>

<p>Karma is just a one variable in this not the final decider.</p>

<p>I guess this breaks the question and no further explaining is needed.Click the link given above and you will understand that Unlike many other beliefs Buddhism does not take away the right of free will because if it did there is no point of a Lord Buddha.</p>

<p>The very core of Buddhism is defying the tide and going against it with ones own free will and courage.So clearly Buddhism is not a fatalism because fate has no power over the will of a "One who is in the path".</p>

<p>Because no matter what he or she will reach nirvana and karma no matter how powerful it is can't change that.</p>
 -1: <p>Fatalism is the error of the ajivika sect of the Buddha's time, which the Buddha unequivocably rejected. That is how we can say that Buddhism is not fatalism. Logically, the reason is that even though our present is conditioned by the unfruited karma of our past, the effective principle of karma is volition or intention, which, being identical with reality (the Absolute), is fundamentally unconditioned and therefore free. The Absolute must be both ignorant and free, because it is (by definition) unconditioned. Primarily ignorant, once it becomes self-reflexive in samsara it becomes self-determining and therefore the cause of future unfruited karmas. This is also the proof of rebirth. Thus the Buddha stated that he knows the past and the present, but the future is indeterminate.</p>
 5380: <p><strong>According to the Buddhism's theory, one man's fate is destined by the past's karma.</strong></p>

<p>This is true that our conditions are determined by past karma, but they are determined by present as well.
A Brahman asked the Buddha in the <a href="http://www.accesstoinsight.org/tipitaka/mn/mn.135.nymo.html">Cula Kammavibhanga Sutta</a></p>

<blockquote>
  <p>Master Gotama, what is the reason, what is the condition, why inferiority and superiority are met with among human beings, among mankind? For one meets with short-lived and long-lived people, sick and healthy people, ugly and beautiful people, insignificant and influential people, poor and rich people, low-born and high-born people, stupid and wise people. What is the reason, what is the condition, why superiority and inferiority are met with among human beings, among mankind?</p>
</blockquote>

<p>The Buddha replies by saying that our conditions are due to our past karma. This; however, is not fatalistic. The idea of karma revolves around the idea that we create our future. </p>

<p>In the <a href="http://www.accesstoinsight.org/tipitaka/mn/mn.101.than.html">Devadaha Sutta</a> the Buddha refutes two Jainism theories about karma </p>

<ol>
<li>The past determines present pleasure and pain, and the present determines future present and pain. </li>
<li>The belief that you can do nothing in the present to get rid of suffering; all one could do is live with it. </li>
</ol>

<p>The Buddha rejected both of those theories that were taught in Jainism. Those two statements sound fatalistic.</p>

<p>The Buddha said that the past and present determine the present; thus, making it not fatalistic. 
Suffering, according to the Buddha, is due to past and present karma as well. 
There is no fatalism in Buddhism. </p>

<p>The karma you mention in your question seems to be more of Jainist theories of karma than Buddhist theories of karma.</p>
