Clutter.
Ugh! I live with it, particularly stockpiling things like old copies of Theater Week and IN Theater which I know I'll never read again but just can't force myself to throw away.
And DVDs, of course. They seem to pile up because it takes a week or more to get through a boxed set of discs and others come in while you're trying to do that.
Even being retired, there aren't enough hours in the day to get everything watched, read, listened to, and studied. It's an endless proposition.