The brain's wiring for persistence gets in the way of cognitive disengagement on a completely unconscious level. Bluma Zeigarnik's experiment, conducted in 1927, was the first to demonstrate how the brain deals with unfinished business-specifically a goal that was consciously selected and then unselected - but its results have been replicated many times since. The experimenters told people to work on jigsaw puzzles and to keep at it until they finished. But some of the participants weren't permitted to finish, and even though they were put to work at other tasks —to distract them from the initial goal and to substitute another in its place -when these participants were tested, they had thought about the unfinished task with twice as much frequency as the other tasks, even though they were told not to think about it. This explains why so many people get stuck in a loop when they quit a goal or situation; it's as though the unconscious is nudging them to go back and finish what they started.