There is an often-told story that when Albert Einstein was once asked what mankind’s greatest invention was, he replied: “Compound interest.” There’s even one claim that Einstein called compound interest the “8th Wonder of the World.”

While there is some debate about whether Einstein really said any of this or not, there’s no question that the compounding of interest is a brilliant thing. As another great American, Benjamin Franklin, described it: “Money makes money. And the money that money makes, makes money.” That is probably the simplest explanation of compound interest you’ll ever hear.

To be fair, compounding interest is a wonderful thing when you are earning it. When you are racking up interest on credit card debt, you’d probably agree with Einstein about it being the most powerful force in the universe.