What Are Fat Fingers and Why Don’t They Go Away?

A momentary 83 percent plunge and rebound in one of Singapore’s largest stocks, Jardine Matheson Holdings Ltd., left dazed traders wondering whether a “fat finger” had struck again in January. After the dust settled, Singapore Exchange Ltd. decided not to cancel the trades, insisting neither human error nor a computer malfunction was to blame. Still, Goldman Sachs and Morgan Stanley were said to have sought to cancel or amend their trades later, indicating mistakes were made somewhere. The episode serves as a reminder that even the best-designed systems can behave unexpectedly once humans enter the equation.

For the origin of the phrase, imagine someone entering a trade and pressing the button next to the one he or she meant to on the keyboard -- literally because his or her finger was too big -- and you get the idea. It’s become a colloquialism that refers generally to human error, either a literal typing error or a more figurative mistake. As many financial institutions have discovered over the years, an extra zero here or there can make a huge difference.