If you want to take it a little deeper, the accumulation of things - material goods and the outward trappings of wealth are all part of the idea that we get some or all of our identity from the things we own. It's been like that down through the ages, building grander and more costly castles and lavish jewelry and clothing and trying to show just how awesome they were based on what they owned, or what they could buy.
The problem is that if you define yourself through what you own, or what you do for a living, is that it is harder to know who that "you" really is if you stripped away all the material trappings. I don't feel the least bit upset about not owning a fast car or a fancy house. They didn't represent me at all other than as a mode of transportation and a place to live. I don't define myself through my stuff. I could care less if someone else has a billion dollar house or if the clothes they wear are dripping with logos and cost the earth, I just kind of feel sad for those people since they're so caught up in the consumerism that what you buy somehow makes you "better." It doesn't. It just masks the person you are inside. And if you're spending gobs of money trying to keep that facade up by buying more and bigger and newer things... that's what keeps you trapped.
I had a coworker that constantly bought a brand new Mustang every other year. She drove it to and from work and for errands. It was awkward to move things in, and she used to complain that it got horrible gas mileage. And yet if you asked her why she kept buying this car, she'd say "Well, I just wouldn't be ME without my Mustang!" What the hell does that mean? She had some idea that the car made her cooler, more awesome, or somehow better? That's screwed up thinking there.
I'm not saying that I live on the side of a hill and have nothing but the clothes on my back - far from it. But over the years I've started appreciating that things are tools - and giving them power over my feelings - whether I'll be devastated if I don't have the latest gadget or someone has something nicer than I do - that's giving away MY power to choose what is important in my life. I have a small, cozy little house in suburbia, a reasonable car to drive, and stuff that makes me happy, but I don't have way more than I need anymore, and I don't give a rat's ass about impressing anyone (except maybe the husband every once in a while). :)
I'd love to actually be a minimalist, and someday that's a possibility. It's taken me some time to break out of my childhood lessons of "save everything" (hoarder/packrat upbringing) but I did get that sorted out, and who knows? I've got time to start culling down the bits and pieces now.