Regardless of how much money a person makes, they think that if they make 10% more, that will take care of their problems, or allow them to be happy. This is not true. More money does not increase happiness, unless the person is being brought up from poverty, which creates genuine improvements in quality of life.
I think this ten percent rule is part of why there is so much resentment to our relatively low tax rates in America. The government isn't just taking away 10% of your money, it's taking away your happiness. No wonder people resent it.