Maybe it's just human nature, at least for some, to take advantage of people who are accommodating.
I tend to go out of my way to avoid conflict and drama, so people sometimes perceive that as weakness. My brother-in-law is a perfect example. He's one of those guys who never helps around the house, and always laughed at me because I do most of the housework. He's unemployed right now, and sits on his butt while his wife is out working, then expects her to cook for him when she gets home. I guess, in his mind, he's more of a man because his wife waits on him.
Anyway, I find more peace by not concerning myself so much with how other people behave. I try to be myself, and if other people take advantage, I eventually just avoid them.