Buffer amount between the value of the collateral and the principal balance of the obligation. For example, if the mortgage has a principal balance of $200,000 and the appraised value of the property is $250,000, the bank has a margin of security of $50,000 in the event of default. The greater the collateral value, the more protection the bank has. In troubled real estate markets because of adverse economic conditions, the market value of the property may fall substantially below the balance of the mortgage. Many homeowners in such a case have defaulted on the loan because of the decline in market values. For example, if the appraised value of a home has fallen to $60,000 while the mortgage balance is $100,000, it might be more financially prudent for the debtor to default on the mortgage.