Definition of 'Regret Theory'
A theory that says people anticipate regret if they make a wrong choice, and take this anticipation into consideration when making decisions. Fear of regret can play a large role in dissuading or motivating someone to do something.
Investopedia explains 'Regret Theory'
In investing, the fear of regret can make investors either risk averse or motivate them to take greater risks. For example, suppose that an investor buys stock in a small growth company based only on a friend's recommendation. After six months, the stock falls to 50% of the purchase price, so the investor sells the stock at a loss. To avoid this regret in the future, the investor will ask questions and research any stocks that his friend recommends.
Conversely, say the investor didn't take the friend's recommendation to buy the stock, but the price increased by 50% rather than decreasing. Thus, to avoid the regret of missing out, the investor will be less risk averse and buy any stocks that his friend recommends in the future.