Then you have desires . All humans do, some more than others. You may desire all of it all at once. Occasionally you cannot control yourself and one of your desires is filled. Therefore you have debt .
Debt makes up the difference between income and expense.
Debt itself is not bad. The problem arises when debt accumulates for no apparent reason. In Bob's case, problems and desires would push his credit card balance upward each month because there is no other place for the money to come from. Since his expenses match income in a normal month, any abnormal spending will go on the credit card. Notice what Bob does not have in the above scenario.