Giles knows it, Graham knows it. Just like calories, our bodies and minds rank physical possessions as more scarce than they are. The result is that we seek too many of them and end up with too many of them.
The extreme reaction is the cold-turkey diet. There's the lifestyle change theory too.
Like food, energy, information and natural resources, this is another symptom of the "good" kind of problem. Modern capitalism has been so mind-boggling successful that many in the world have a new problem: they lack the mental circuitry to handle having more than they need of so many of the things that they want.
This is definitely a problem and we post-industrial societies are going to need to find a solution, but we should all remember that it's the good kind problem. Better this than the problems encountered last year by folks in Haiti or Pakistan.