Lessons learned : you must be tough to the point where you disgust yourself; humans are even worse than you thought; contracts are a must (like in "whatever you do, even if you're saving the world for free, selling your mother")
Meta lesson : managing humans implies stopping being human. If you don't, then you expose yourself to a lot of disappointment and stress... It doesn't mean treating people like shit, it means you break all the bridges between you and them; bye bye empathy, love, etc. The question is : do you want to be that ?
And in case you don't know, stress means : perpetually exhausted (that is, you don't have a life beside your job, that is 0 quality time with your wife or children and then you end up wondering "they've grown so much and I don't know them"); pain in every part of the body (that is, even when doing your super job, you aches; blood pressure go up, which means you'll be dead at 40; you get sick much quicker; bad sleep which implies bad health). So stress does hurt.
But somehow, I still want to do it : the need for freedom is so big I can't give up :-)