Norman has a brilliant response to "But we might need that, and then we'll feel terrible if we got rid of it!" He says, "I'll put this in a special box in the attic. If you need it in the next year, it'll be right there, and you can have it. If you don't need it in the next year, then we can probably get along without it, and I'll donate it to charity."

Your apartment probably doesn't have an attic, but a box under the bed -- or something like that -- could probably serve a similar function. And if a year is too short, it could be two years or three or five. Put a post-it note on the item with the date that it went in the box, and once a year, give away whichever things are still in the box whose post-its show they're past the keep time that you've set.

Of course, this works for me because Norman is there encouraging me to part with stuff; I don't know how it goes if you have to be your own encourager. :-)