Next time you're projecting a completion date for a work project, do yourself a favor. Build in some extra time.
People habitually underestimate the time it takes to finish tasks, says a team of psychologists. And they make this mistake no matter how simple the job. The researchers asked undergraduates to predict when they would complete a variety of projects—from writing a thesis to fixing a bicycle. Inevitably, the students took longer to finish than predicted. On average, their estimates fell short by about three weeks for long-term endeavors and by a few days for briefer undertakings, reports Roger Buehler, Ph.D., of Simon Fraser University, and colleagues.
The tendency to underestimate task time is evidence of an "optimistic bias." It stems from the information people consider—and ignore—when making their forecasts. "People focus very little on their relevant experience. Instead they focus primarily on their future plans," Buehler says. So even though previous projects might have run into roadblocks, prediction runs forward, oblivious to potential obstacles. And that leads folks to assume that their plans will go smoothly.