A couple more reasons I can think of for quitting:

• The old dog syndrome: Anything I do isn't on the same quality level as everyone else, I better quit and find some easier trash cans to scrounge at.
• Bad ethics: Possible examples: The company keeps spilling oil in the bay or pushing pipelines through or buying up futures contracts on grain and pulling 200 percent profit from food leading indirectly to the starvation of many children.