Compound Interest

"You work 40 or so hours per week, but interest works 168 hours per week against you. You stop for food and water, interest never stops. It may be small amounts if your balances are low, but taken over a lifetime, compound interest will own you. You have to break the cycle and get rid of your debts."

http://quitbeinglazy.com/2009/12/interest-the-most-powerful-force-in-the-universe/