Sometimes people invest irrationally based on psychological biases rather than market fundamentals. When a specific stock’s price is rising or when the overall market is rising, they buy. They see that if they had invested 12 weeks ago, they could have earned 15% by now, and they develop a fear of missing out.
Conversely, when a stock’s price is falling or when the overall market is declining, loss aversion compels people to sell their stocks. So instead of keeping their losses on paper and waiting for the market to change directions, they accept a certain loss by selling. Such investor behavior is so widespread that it affects the prices of individual stocks, exacerbating both upward and downward market movements creating excessive moves.