Base Rate Fallacy

This is the investment equivalent of saying your fave football team is terrible, and burning your jersey because they lost one game to an inferior opponent, even though they're now 9-1. You're basing too much of your judgment of your team's quality on a single, recent event (the loss) and ignoring the fact that they have a great quarterback, a stout defense, and a Hall of Fame coach.

Investors who look at one poor quarter of performance as a basis for not investing, thereby ignoring tons of long-standing info about the company's market position and overall strength, are guilty of falling for the base rate fallacy.