Front-runners are usually focused on racing each other. They often do not realize that when people cannot decide between two leading candidates -- and it doesn't matter whether we are talking about politicians or consumer appliances -- our decision can be subtly swayed by whoever is in third place.

Psychologists call this the decoy effect: In a perfectly rational world, third candidates should only siphon votes away from one or both of the leading contenders. Under no circumstances should they cause the vote share of either front-runner to increase. In the actual world, however, third candidates regularly have the unintended effect of making one of the front-runners look better than before in the minds of undecided voters.