You know what I'm talking about. You do something stupid and get a big ol' bloody, oozy scrape. After a little while, it finally starts to heal over and form a nice, thick scab.
And you Can't. Stop. Thinking about it!
It itches and catches on things, and you keep finding yourself subconsciously rubbing at it. Eventually, you give in and start picking at it in earnest, working at it until you've peeled the darn thing off.
And then you start bleeding again. Of course.