Concerning "Stuff"

Stuff used to be more difficult and expensive to manufacture, so people would accumulate all they could. Basically, stuff used to be more valuable. Over the past century, stuff has become so mass-produced that it doesn't cost much to fill a house with it. Unfortunately, people haven't adjusted their values accordingly, so they actually do fill houses with it, usually to their own detriment.

As usual, Paul Graham has hit the nail on the head, this time regarding "stuff" - why we overvalue material possessions, collect too many of them, and let them exhaust us mentally:

...unless you're extremely organized, a house full of stuff can be very depressing. A cluttered room saps one's spirits. One reason, obviously, is that there's less room for people in a room full of stuff. But there's more going on than that. I think humans constantly scan their environment to build a mental model of what's around them. And the harder a scene is to parse, the less energy you have left for conscious thoughts. A cluttered room is literally exhausting.