After six years of life in US, I had a deep realization认识到 that the US economy is based on people's confidence信心 of spending their money.  "Ｗe still can shop without having any money in a short term, that's what credit card is for."  When American teenagers年轻人 turn 18 years old, they can get their first credit card信用卡 right way.  We can imagine想像 what teenagers would do with hundreds or thousands of dollars. Of course, they SPEND!