When I was a freshman in high school, I was playing basketball one day during lunch. This was an outdoor court, made of concrete, where the edges of the court were lower than the court itself. Well, I jumped out of bounds to save the ball, and landed on the concrete on my left shoulder. Well, it ended up being just a sprain, but my shoulder and my collar bone never seemed to meet up quite right after that.
Fast forward to my junior year. This time no dangerous sports for me, I was on stage. I was an umpire in a pantomime scene. Well, since there are no spoken words, you're supposed to "over do it" with pantomime. Well, I over did it alright. I threw the player out of the game in the scene, and re-sprained my shoulder. Well, it used to ache and occasionally have problems, but it's not bothered me in a long time.
So who reminded my bad shoulder that it was bad?