a lesson
Examples
I was walking down fifth avenue today and I found a wallet, and I was gonna keep it, rather than return it, but I thought: well, if I lost a hundred and fifty dollars, how would I feel? And I realized I would want to be taught a lesson.
Here is a lesson in creative writing. First rule: Do not use semicolons. They are transvestite hermaphrodites representing absolutely nothing. All they do is show you've been to college.
A lesson taught with humor is a lesson retained.
I learned to walk as a baby and I haven't had a lesson since.
He who falls, teaches others a lesson.
Hunger teaches us many a lesson.