Greater fool theory
The greater fool theory states that the price of an object is determined not by its intrinsic value, but rather by irrational beliefs and expectations of market participants. A price can be justified by a rational buyer under the belief that another party is willing to pay an even higher price. In other words, one may pay a price that seems "foolishly" high because one may rationally have the expectation that the item can be resold to a "greater fool" later.
Examples
In real estate, the greater fool theory can drive investment under the expectation that prices always rise. A period of rising prices may cause lenders to underestimate the risk of default.
In the stock market, the greater fool theory applies when many investors make a questionable investment, with the assumption that they will be able to sell it later to "a greater fool". In other words, they buy something not because they believe that it is worth the price, but rather because they believe that they will be able to sell it to someone else at an even higher price. It is also called survivor investing. It is similar in concept to the Keynesian beauty contest principle of stock investing.
