I'm sure everyone has their own approach to the creation of characters. I always chose to create a character "sketch"; a psychological profile of sorts. What made them tick? What were their beliefs, their motivations, their fears? What were their weaknesses and strengths? How did they speak? What was their choice of fashion? I wrote small backstories for each character so that -I- knew them.
Assuming you will ever come to some Buddha-knowledge about the inner-machinations of the human condition by virtue of life-experience will probably leave you ultimately feeling like a failure. Many people with similar backgrounds and underlying issues achieve very different outcomes due to circumstances, random events, environment, sheer will and pure luck. As a writer, you have the opportunity to CREATE the motivation (cause) and DICTATE the action (effect) at whatever levels of complexity you choose with your prose. As long as you're honest about the characters you choose to conjure, in situations you are qualified to create, then you'll be just fine.
Finally, I think writing is like a snapshot. It captures not only whatever the writer is trying to present, but it is also a snapshot of the author and their view of things at that particular moment in life. If an author chose to write the same story over and over, at five year intervals, it would likely always be different; not just in words on a page but in the general tone and viewpoint. None of them would be wrong, just different because of the time-in-life it was written. Artists reflect life and the angle at which the mirror is held varies as the author grows, but the reflection is always a valid one.