Too many credit cards
Pack your wallet full of credit cards and you could be limiting the amount you can end up borrowing for something really important like a mortgage. All those credit limits are considered part of your debt. Even if your balances are at zero, lenders take into account all that credit you could use for whatever you want whenever you want. Four credit cards each with $2,500 balances will hinder your borrowing potential to the tune of $10,000.