If offered a Snickers, a Milky Way and an Almond Joy, participants would always choose the Snickers. But if they were offered 20 candy bars, including a Snickers, the choice became less clear. They would sometimes pick something other than the Snickers, even though it was still their favorite. When Glimcher would remove all the choices except the Snickers and the selected candy, participants would wonder why they hadn’t chosen their favorite.
Turns out that the brain is an expensive thing to run. If you want to dig deeper, here’s your entrance to the rabbit hole: a fascinating article on the Neuroscience Behind Bad Decisions.