control

I think there are two sources of control: you think you know better and/or you're insecure

a friend doesn't want to donate money to another friend in need because she doesn't think he's made good decisions with his money so far. if he had planned better he might not be in the current situation. so in giving him more money, her money, he might also waste that money, her money.

well, sure. but once you give something away, it's no longer yours. maybe you're not financing their poor habits, but you're helping them be the person that you enjoy, the person you're friends with. stress of not having money will probably change them, make them less happy, less nice, less pleasant to be around. 

on the other side, are those who don't think they know better, but who are insecure and don't think they can keep you otherwise. so they hold on tight. the jealous type in relationships embodies this type of control.