Modern psychology and neuroscience has essentially distilled the behaviour of human beings into a combination of genetics, experiences, and circumstances. If you know all of these things, then a person’s behaviour is arguably deterministic in nature. So then, what of the age old concept of free will?
Well, this would be a problem for the very notion of free will, except for simple consideration that while genetics, experiences, and circumstances can identify what decision would be made in a situation where the agent has perfect information, the reality is that in the absence of such knowledge, the agent is left with only probabilities rather than having a concrete decision.
It is possible to show that perfect information is impossible for a normal agent with a simple thought experiment. Consider two mutually exclusive choices, the effects of which are unknown. In order to find out the effects of one choice, an agent must eliminate the possibility of knowing the effects of the other choice. Thus, it becomes impossible to know both things at once.
Thus, in all decisions made, there must exist uncertainty to some degree, which means that the decision is ultimately made as an informed, but not predetermined choice.