Money is a formal token of delayed reciprocal altruism; a famous statement by Richard Dawkins.

What does that mean?

Simple. When you get paid, that's gratitude you are receiving. When you pay, that's gratitude you're expressing.

Before money, people stored debts of gratitude in their heads, and used cumbersome barter to pay or collect those debts. After money, that inevitable fact of human life got greatly streamlined and sped up.

This conceptualization of money is the cornerstone of civilization. If you don't understand money as the above, you are going to have a very, very difficult time being successful in the world today.

I'll now leave you with what, perhaps, is the greatest essay on money ever.