We are who we are as a result of the combined effects of nature and nurture (or lack thereof)—genetics and environment—with genetics having the dominant role.
We have absolutely no hope at all of self-determination until we are a mid-teenager at best, and by then our personality is largely set. If, after that, we have any hope of becoming who we think we want to be, it will only happen with great effort and introspection. That look in the mirror is more than most of us can handle and the work involved is more than most people can bear or are willing to do. So the vast majority of humans are destined to be nothing more or less than who and what their parents made them—for better or for worse as their parents before them.
We are all largely the products of decisions that were not well thought out: emotional reactions made in haste with little, if any, reflection or contemplation of the possible consequences or results.
This is the history of humanity. The few exceptions are notable for being few and far between.