On the one hand I think you are at least partly right, but I also think about the saying: "opportunity makes a thief" which, I think is also at least partly true
Yes, certainly, it's both, you're right. We are to an extent shaped by our experiences. For example someone who has risen to a position of absolute power might see everyone else as inferior to him*, including those people whom, prior to his reaching that position, he viewed as colleagues and equals. It's both nature and nurture, it's not 'either/or', it's 'and'.
*
it always seems to be a 'him'.