I've been committed to decluttering in theory ever since I helped clean out my parents' house after my mother died. They were by no means hoarders, and Mom kept a very neat house, but they had that Depression-era childhood thing going on where they didn't like to get rid of anything that might possibly be useful. There were two desk drawers entirely filled with blank greeting cards of various kinds, and while we have a large extended family and my parents had a reasonable number of close friends, no one sends THAT many Get Well/Christmas/Thank-You/etc. cards.
The problem is finding/making time for it. Also, with books, letters, and pictures, there's the fear that someday I really WILL write that book set during Napoleon's invasion of Russia, and then where will I be if I donated that half-shelf of research materials I bought for it years ago? And what if elderly me wants to re-read all those letters from college friends or look at all those pictures from childhood vacations that so far young adult and middle-aged me has been content to leave in boxes in the basement?
Which is silly. I have full access to the internet and an extensive academic library (through work) to research anything I want to write about. And elderly me will still be ME. She won't want to discard her most cherished memories and heirlooms, but she's unlikely to grow a complete new personality and suddenly care more about those boxes in the basement than reading or traveling (assuming she's healthy enough to do so).
It also helps me to imagine some hopefully far-future Annabel having to sort this stuff out, and thinking, "Why did Mom KEEP this?" instead of, "Is there the tiniest possibility that I ever might regret getting rid of it?"