"Oh, I don't have that much stuff. The move should be a snap."
When I was in grad school, I moved six times in eight years. Or was it seven times? I forget. But roughly once every year and change. When you do that, you don't ever get a chance to accumulate that much stuff. And everything you have is disposable, more or less.
By contrast: I have been in my current apartment for twelve years.
Granted, there was the year I spent at Fellowship U. back in 2007/08. But I had a subletter then, so all I had to do was move my personal stuff into the back storage closet and box up the few things I was taking with me. So, twelve years since a move. This by far the longest I have lived in any single address since I... well, I was going to say "since I lived with my parents," but it occurs to me that my family moved across town when I was seven, and I moved out when I was eighteen. So: the longest I have lived anywhere, ever.
You all know what that means: even though I've only got a little over 500 square feet, and even though I like to keep a lot of empty floor space in that space so I don't feel crowded, in twelve years, you accumulate a lot of stuff without even realizing it.
And when you finally move, even the tiniest space turns into a clown car: you keep pulling stuff out and putting it in boxes, and yet there always seems to be more -- way more than the space and the laws of physics would seem to allow. How is this possible?!?