As you get older, you become more like your
parents. You didn't mean for it to happen. You didn't want it to happen. You swore that you wouldn't let it happed. But it happened. You got more
conservative, gained weight, got married, bought a
Volvo, and before you knew it, you were shouting at the kids to
turn that crap down.
The classic example is given by Abraham J. Simpson, "I used to be with it, then they changed what it was. Now what's 'it' is wierd and scary to me. It'll happen to you!" And eventually it did happen to his son Homer, "I used to rock and roll all night and party everyday. Then is was every other day. Now, I'm lucky if I can find half an hour a week in which to get funky."
This is not to be mistaken with the science fiction concept of killing your father or grandfather.