There's a really cool graph I first saw in a book many moons ago.

It's from Your Money or Your Life, one of the books that changed how I think about money. (I highly recommend it ... except for what it teaches about investing.)

Vicki talks about diminishing returns. That when we spend on our survival (food, water, shelter, clothing) there is a very high return. But as we move from survival to comforts, and then to luxuries, we have to spend much more to gain more fulfilment.

This is the law of diminishing returns.