I don't think this is just about boys, i'm a girl!
I am not suggesting all kids NEED to do this to learn about the world, but many do. Truly, not every child learns their limits the same way.
I grew up on a farm and my mother was a realist but a compassionate one. We ate the meat we raised, but all our animals were treated kindly and their deaths were as qick and painless as possible. I was taught the reality of being a meat-eater but i wa NOT allowed to torture animals or insects (i was once stung 4 times within 9 minutes by a wasp when i was 3 or 4 years old and my mother released it when she managed to catch it! She was NOT without compassion!). My parents modelled humane compassionate behaviour, but i didn't know where my limits were until i tested them.
That might seem very odd to some who know because they were TOLD that it's wrong to kill, i had to FEEL how wrong it was. I can remember once killing a mouse i found injured in a trap and i felt sick with myself for a month. Even though the mouse was already trapped and couldn't have been released, the fact thet it was *ME* that killed it...i felt disgusted, repelled with myself.
I'm afraid i've continued to be the sort of person that needs to experience something to really respect it. I knew from before my daughter was born that i didn't want to be someone who smacks, but you know what, it took me getting to the end of my rope and smacking her hand to learn the internal motivation i KNOW i can rely on. Before that day i was trying not to. NOw i know how wretched it REALLY feels to do that i don't even need to try, i am internally repelled from striking her.
Perhaps some people can control their emotions. I cannot, and thus i have had to learn how to control my responses to them. I deeply regret the mindless cruelties i inflicted on the creatures i hurt, but i do not accept that doing so means i was and am demonic. I am a person, and an imperfect one at that.