Ego

Part of our minds—our egos—assure us that our assessments were correct and everybody else will eventually see this stock price moving in the direction that we first anticipated. Unlike making a decision to buy a car, a book, a vacuum cleaner, or anything else that required a one-time decision about the expenditure of funds, investments have an additional emotionally debilitating element. The decision process continues each tick after the initial
purchase. You buy a stock and the price immediately goes down. Do you sell it here or is it at the bottom? It keeps going down, the same question occurs every day, every tick. Conversely, the stock price is going up. Is it time to take profits?
How embarrassing it would be if it went back down to where you bought it. Or worse, if after it was up at this price, you eventually sold the position for a loss. Each position becomes an emotional conquest—your intellect versus the rest of the market players.