Perception of choice
"If you are given a choice, you believe you have acted freely. This is one of the darkest of all psychological secrets."
-- " said Teller, of the duo Penn and Teller, to Smithsonian magazine.
Another dark psychological secret magicians routinely take advantage of is known as change blindness -- the failure to detect changes in consecutive scenes. One of the most beautiful demonstrations is an experiment conducted by the psychologist Daniel Simons in which he had an experimenter stop random strangers on the street and ask for directions.
Midway through the conversation, a pair of confederates walked between them and blocked the stranger's view, and the experimenter switched places with one of the stooges. Moments later, the stranger was talking to a completely different person -- yet strange as it may sound, most didn't notice.