How Credit Card Companies Make Money (And You're Not)

Do you actually know how much interest you paid last year? Do you know your card's real APR, or just the number you assume it is? Ever wondered why your card pays you to spend on it? Do you know who's really paying for those rewards? Does it change anything if you pay cash instead of card?

This is how credit card companies actually make money, and why the person paying cash is funding someone else's rewards.