Adverse selection occurs when one party in a transaction has more or better information than the other party, often leading to the more informed party exploiting the situation. In this case, the bank customer chooses a mortgage with low initial payments, knowing she will have trouble making early payments. The bank, using standard default assumptions for ordinary mortgages, underestimates the risk of default, thus exposing itself to adverse selection, where the higher-risk borrowers are more likely to select this type of mortgage.