How is it that people come from similar situations yet feel completely different emotions?

Like children of divorce? Some are all “I’ll never get married!” and others want nothing more than to start a family.

Or children of alcoholics? Some become responsible, some completely irresponsible.

Or those who are raped? What makes some people kill out of revenge and some people not?

not comparing any of these! just to be straight… these are just things that have been on my mind

How do these things happen? Is there some solid explanation?