They melted down and dragged economies and political establishments with them. By definition, pyramid schemes are doomed to failure. The number of new "investors" - and the new money they make available to the pyramid's organizers - is limited. When the funds run out and the old investors can no longer be paid, panic ensues. In a classic "run on the bank", everyone attempts to draw his money simultaneously. Even healthy banks - a distant relative of pyramid schemes - cannot cope with such stampedes. Some of the money is invested long-term, or lent. Few financial institutions keep more than 10 percent of their deposits in liquid on-call reserves. Studies repeatedly demonstrated that investors in pyramid schemes realize their dubious nature and stand forewarned by the collapse of other contemporaneous scams. But they are swayed by recurrent promises that they could draw their money at will ("liquidity") and, in the meantime, receive alluring returns on it ("capital gains", "interest payments", "profits"). People know that they are likelier to lose all or part of their money as time passes. But they convince themselves that they can outwit the organizers of the pyramid, that their withdrawals of profits or interest payments prior to the inevitable collapse will more than amply compensate them for the loss of their money. Many believe that they will succeed to accurately time the extraction of their original investment based on - mostly useless and superstitious - "warning signs".