The U.S. economy may be bouncing back nicely, but way too many households still struggle every month just to keep up with the bills. If your expenses are greater than your income, the inevitable result is ever-mounting debt -- usually on credit cards. Indeed, a recent LendingTree survey found that 42% of Americans who are carrying credit card debt got into debt in the first place while simply trying to make ends meet.And that's just one of the common reasons why people end up in debt that they can't pay off.