He was originally going to direct Rain Man (1988) but abruptly bailed when production was due to start due to "creative differences". Steven Spielberg stepped in but left after a few months, followed by Sydney Pollack who eventually left as well, leaving the project without a director until Barry Levinson signed on.
I think people who make movies start out with kind of lofty ideals. But it's work that conspires to put you into a cold, clinical professional mode very quickly. What I keep telling myself is that in making any movie, I've got to reflect and convey to the people I work with the reasons why I wanted to get into the business in the first place.