Good bosses are a good deal better than bad ones. Replacing a supervisor from the bottom 10 percent of the pool with one from the top 10 percent increases output about as much as adding a 10th worker to a nine-worker team.
That it's better to have a good manager than a poor one isn't very surprising. But the authors' two other findings are a bit more striking. The main impact effective supervisors have on their employees doesn't come from motivating or supervising them per se, it comes from teaching them better work methods.