Bill Watterson, the creator of Calvin & Hobbes, recently gave his first interview in 20 years. He explains why he stopped when he did:
If I had rolled along with the strip's popularity and repeated myself for another five, 10 or 20 years, the people now "grieving" for "Calvin and Hobbes" would be wishing me dead and cursing newspapers for running tedious, ancient strips like mine instead of acquiring fresher, livelier talent. And I'd be agreeing with them.
I think some of the reason "Calvin and Hobbes" still finds an audience today is because I chose not to run the wheels off it.
I've never regretted stopping when I did.