When the Nobel Prize-winning psychologist Daniel Kahneman was a young man, he led a committee to write a new part of the curriculum for Israeli high schools. The committee worked for a year, and Kahneman asked his colleagues how long they thought the rest of the project would take. Their estimates were around two years.

Kahneman then asked the most experienced among them how long such work took other curriculum committees. The gentleman pointed out that roughly 40 percent of the committees never finished their work at all.

But what about those that did finish? The gentleman reported that he had never seen a committee finish in less than seven years and never in more than 10.

This was bad news. They might fail to finish a task that they thought would be done in three years. At best, the project might consume eight or nine years. Yet this information didn’t affect those on the team at all. They carried on, assuming that though others might fail or dally, surely they wouldn’t.