This is really true, because I noticed that after I found additional work in business, my standard of living improved only a little, very little. And I am very surprised, because today I would not be able to live on the money that I used to earn. This is obviously connected with the very high price level and perhaps my needs have grown a little, but in general I am shocked that today it is almost impossible for a person who has only one source of income to live, especially with a family.
I can explain that with people adopting to situation. If you earn $1000, spend $900 and you feel like you cant afford a lot. They you find another job or get a raise and start earning $2000, you will still be in a situation that you can afford a lot, because your expenses also increase to level of your salary. And its not because prices have increased, its because not matter how much people earn, they often happen to spend whole salary.