How Big Things Get Done: The Surprising Factors Behind Every Successful Project, from Home Renovations to Space Exploration

by Professor Bent Flyvbjerg

In one study, researchers asked students to estimate how long it would take them to finish various academic and personal tasks and then asked them to break down their estimates by confidence level—meaning that someone might say she was 50 percent confident of finishing in a week, 60 percent confident of being done in two weeks, and so on, all the way up to 99 percent confidence. Incredibly, when people said there was a 99 percent probability that they would be done—that it was virtually certain—only 45 percent actually finished by that time.19 For us to be so consistently wrong, we must consistently ignore experience.