...
Lightening
Fatigue / heated out
Course conditions too poor (mud mostly)
Tension within a group and I bail
Partner needed to go, left when they did
Join up at another course
Got dark
Got hungry
A buddy got hit by a disc, felt that was a good reason to not stick around. But I've left a couple out of frustration of searching, losing a favorite disc, and heavy rain (I'll throw in a light rain.) never left when money is on the line or tourney/league play though. Only casual.