A credit card is essentially a loan from a bank that can be taken out at any time during your discretion. When you use credit, you are effectively taking out a loan against the issuer of the credit card. Therefore, you have an obligation to pay that debt. A credit card issuer will impose a credit limit on you according to your credit score and credit history. Those with a bad credit score will usually have a low credit limit as well as those without a credit history. This is because there is always an inherent risk in loaning someone money.