I got to work with Robert DeNiro once and it was a strange experience. Gwyneth Paltrow and I were doing Great Expectations movie together and we were complaining about what a mediocre film experience it was. DeNiro showed up on set and all of a sudden the director got better, the director of photography got better - everybody got more interested and excited. DeNiro isn't waiting for other people to create the environment that he wants, he brings it along with him.
Friends can hurt you, but the possibility of pain with lovers is so much greater because your expectations are so high. You don't ask as much of your friends.