The free will concept is central to any human behaviour theory. Our
pretended free will is very relative. As humans we struggle between our
tendencies (desires, drives, that are more or less secret according to
social acceptance), and our rational capacity of evaluating which is the
best choice we can make in a given circumstance. Some times we make a
very thoughtful choice, but others, especially in very emotional or
stressing ocasions, we make choices that we may deeply regret later.
In this struggle we are choosing between two main "suggestions" for
responding, one commanded by our primary brain (instinctive) and the
other by our secondary brain (rational). The more stressful
circumstances are, the more predominant our primary brain will get.
As the behavior we finally decide will be the result of this struggle,
which can be more or less intense and/or stressed according to
circumstances, we can logicaly conclude that there are a lot of
instances when there is no full free will available for us.