The more bad you feel as a kid, the more intense becomes the desire to escape it, thus you're willing to work harder for it.
I think the number of peculiar personal features in Hitler, Mao, Stalin etc., comes from the number of experiences they had in life - bad experiences, something that really changed their look at someone, something. Not unsual. A lot of these prejudices, features often become irrational, though. Not usual, either.
But yet you can't properly apply a pattern which is universal when dealing with human beings - the upbringing is far from the only factor deciding one's course of life. Watched this program once, about human cannibals. One of the cannibals, forgot his name, had a totally normal childhood - with a warm, kind, and caring family. But when he started to bring home dead animals run over by traffic, and henceforth began to cut them up - his family started wondering. His father, a chemist, IIRC, taught him how to preserve bones, and that's when things got in motion.
He developed this desire to kill people and preserve them. He killed a lot of people, kept head, legs, and other body parts in his fridge and then ate them over a period of time. My point here is that the boy/man, he a completely normal infancy and childhood - but along with the rest of his fellow cannibals around the world - they all had one common deficiency: lack of activity in the frontal lobe, which simply meant that they were wholly incapable of feeling something for other people, i.e., love, grief, sorrow, emotional distress you name it. Shocking.
