The Christmas tree problem

Leidy Klotz, an engineering and architecture professor at the University of Virginia, has shown that humans reflexively add when trying to solve problems: more people, more money, more features, more stuff, even when subtracting would work better. In one demonstration, adults were given a Lego structure that needed to be strengthened to hold a masonry brick above a Star Wars stormtrooper.

Each problem solver could earn money by completing the task, but there was a catch: every Lego piece they added reduced their reward. And yet most people added pieces, even though removing a single, obviously precarious piece would have solved the problem instantly.