If that were all there were to life, Bob would be set to some degree, because in this example expenses exactly match income. You have problems . For example, you get a speeding ticket one day. Or you lose your job. 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.