Gas and oil, and used oil

Gasoline makes the car go.
Money is like gasoline for the economy.
As a driver, you keep it in mind all the time.

Oil is like credit.
We need it to make the car go, to make the economy go.
But we think about it less often.

Debt is like used oil drained from your engine and stored in sloppy jugs that you have to keep in the trunk of the car, and carry with you all the time.