This happens for one of two reasons. First, people overstated their expenses. If you did this, you need to go back and lower your expenses.
Second, people forget to mention the money they receive from someone to cover their living expenses such as rent and food. These should be listed as outside contributions. Even if someone else pays for these things directly and you don't receive this cash, you need to tell us how much the things they pay for are worth.
For example, say you don't pay rent because you live at your mother's house, and your mother's rent is $1000/month. You may estimate that your mother pays $500/month in rent for you. You should list this as a $500/month in an outside contribution.