Whether it's a waiter recalling a long order, a meaningful consumer transaction or a cliffhanger on Netflix, tasks heavily occupy our minds until complete.
Bluma Wulfovna Zeigarnik (1901 – 1988) was a Soviet psychologist and psychiatrist. She first studied the phenomenon after her professor noticed that a waiter had better recollections of still unpaid orders. However, after the completion of the task – after everyone had paid – he was unable to remember any more details of the orders!
The effect can explained by looking at Lewin’s field theory: a task that has already been started establishes a task-specific tension, which improves cognitive access to any relevant information.
This tension that has been established is relieved upon successful completion of the task. If the task is interrupted, any reduction of tension is impeded. With continuous tension, the relevant information is becomes more accessible and more easily remembered.
The Zeigarnik effect suggests that students who temporarily stop their studies, during which they do unrelated activities (such as studying unrelated subjects or playing games), will remember material better than students who complete study sessions without a break (Zeigarnik, 1927; McKinney 1935).