In late January 2021, GameStop traded at \$483 a share intraday — up roughly 15x in three weeks on the back of a coordinated retail-driven short squeeze. By mid-February it had fallen to \$40. Every retail investor who bought at \$300 in 'because everyone was talking about it' lost roughly 87% in three weeks.

Two years earlier, in February-March 2020, the S&P 500 fell 34% in 33 days as retail investors panic-sold their accounts. By August 2020, the index had fully recovered. The investors who held returned to even; the ones who sold near the lows locked in losses they could never recover.

Both episodes are the same bias in different directions: the human instinct to do what the crowd is doing, accelerated by the velocity of modern markets and amplified by social media. Following the herd is the most expensive consistent mistake in retail investing.