Why do banks suffer from bankruptcy?

Why do banks suffer from bankruptcy?
In it's most basic sense, banking is simply taking deposits, paying interest on those deposits, then lending that money to others and collecting a higher rate of interest on those loans -- then keeping the difference. When this economy hit a rough patch, those folks cannot pay back those loans, so the bank loses the interest income AND has to charge off the bad debt (an expense). Both of those items make it more difficult to pay the interest to the depositors. This is a very simplified version, but meant to equate it to your own family budget. If your income suddenly decreased (the interest income from the loans) and your expenses increased (the bad loans written off) and you still had to pay your other expenses (the interest paid on the deposits), sooner or later you are going to be in the hole.