We must not misunderstand that karma is fatalistic or deterministic.
and I think this is v important to consider:
"Listen, Sivaka. Some kinds of feeling arise with bile as condition ... with changes in the weather as condition ... with inconstant behavior as condition ... with danger from an external source as condition ... with kamma-results as condition. Any ascetic or Brahmin who is of the view that, 'All feeling is entirely caused by previous kamma,' I say is mistaken."[44](also note that there are five kinds of conditionings, see
http://www.geocities.com/Athens/Academy/9280/kamma1.htm)
And yes our thoughts and behavior are not predetermined. They are arising conditions, but they are not 'predetermined' by anything, because if it were, then as the Buddha said (
Misunderstandings of the Law of Karma):
"Bhikkhus, of those three groups of ascetics and Brahmins, I approach the first group and ask, 'I hear that you uphold this teaching and view ... Is that so?' If those ascetics and Brahmins, on being thus questioned by me, answer that it is so, then I say to them, 'If that is so, then you have killed living beings as a result of kamma committed in a previous time, have stolen as a result of kamma done at a previous time, have engaged in sexual misconduct ... have uttered false speech ... have held wrong view as a result of kamma done in a previous time.'(cont.)...These words discourage us from going too far with kamma by considering it as entirely a thing of the past. Such a view encourages inactivity; passively waiting for the results of old kamma to ripen and taking things as they come without thinking to correct or improve them. This is a harmful form of wrong view, as can be seen from the Buddha's words above.
Significantly, in the above passage, the Buddha asserts effort and motivation as the crucial factors in deciding the ethical value of these various teachings on kamma.
The Buddha did not dismiss the importance of previous kamma, because it does play a part in the cause and effect process, and thus has an effect on the present in its capacity as one of the conditioning factors. But it is simply one of those conditions, it is not a supernatural force to be clung to or submitted to passively. An understanding of the Principle of Dependent Origination and the cause and effect process will clarify this.
For example, if a man climbs to the third floor of a building, it is undeniably true that his arriving is a result of past action -- namely, walking up the stairs. And having arrived there, it is impossible for him to reach out and touch the ground with his hand, or to drive a car around. Obviously, this is because he has gone up to the third floor. Or, having arrived at the third floor, whether he is too exhausted to continue is also related to having walked up the stairs. His arrival there, the things he is able to do there and the situations he is likely to encounter, are all certainly related to the "old kamma" of having walked up the stairs. But exactly which actions he will perform, his reactions to the situations which he meets there, whether he will take a rest, walk on, or walk back down the stairs and out of that building, are all matters which he can decide for himself in that present moment, for which he will also reap the results. Even though the action of walking up the stairs may still be influencing him (for example, with his strength sapped he may be unable to function efficiently in any given situation), whether he decides to give in to that tiredness or try to overcome it are all matters which he can decide for himself in the present moment.
Therefore, old kamma should be understood in its relation to the whole cause and effect process. In terms of ethical practice, to understand the cause and effect process is to be able to learn from old kamma, understanding the situation at hand, and to skillfully make a plan of action for improving on and preparing for the future...