When a person without a long history of paying his or her bills on time wants to obtain a loan to purchase a home or car, lenders are often reluctant to take the financial risk. Without a track record, that person’s promise to repay what he borrows is insufficient for the bank. The would-be borrower usually resorts to finding someone who does have a history of making good on their debts, asking them to put their name on the loan too. The co-signer’s promise assures the lender the loan will be repaid.

When someone makes a promise to us—whether for financial,…