Fractional reserve banking as a banking system in which banks normally retain less money(Liquid assets) than their depositors have right to claim. we noted that fractional reserve banking is nothing new, it has exited since ancient times. the fractional reserve system enhances the potential profitability of banks, but we noted that it is associated with one major problem, a problem so serious as the sometimes threaten the continued existence of the bank. WHAT IS THIS ONE MOST SERIOUS PROBLEM?