Buy at low price and sell at high price. This is expected of all investors but it is difficult to execute. It is easy to say whether a certain price is low or high in retrospect, but in the moment, it is monumentally difficult. Prices affect the psychology and emotions of market participants. Traders and investors must have a certain objective method to determine if prices are high or low. Humans are conditioned to follow the crowd. There is inherent difficulty in consistently buying low and selling high. When prices are low, sentiment tends to be overwhelmingly negative towards a stock. Many bullish holders are forced to dump their shares. Similarly, when price is high, it is difficult to conceive of letting go of a winner.