It’s who has to prove what in any lawsuit. For example, if you are sued for a credit card debt, even if you did have a credit card, they will have to prove the following:

• you used the specific credit card (number) account;
• they are the people who issued the credit card;
• if they are not the people who issued the credit card, that they have the right to collect on the account (if they bought the account, they have to prove each and every step of that transaction to prove their right to collect)
• the exact amount they say you owe, including each and every fee
• their right to interest, the amount of interest, their right to attorney’s fees
• the accuracy of the calculation of interest (annual, quarterly, daily compounding etc.)
• how much you paid on the account, when they gave you credit for those payments