"I remember interrupted or ongoing tasks and problems more easily than I remember ones that are completed or solved."
An interrupted task or an unsolved problem has a privileged status in memory, compared to completed ones. More people remember interrupted or unfinished tasks than finished ones. Tasks that are left unfinished are also remembered in much more detail.
A waiter in a restaurant can remember large quantities of diverse details regarding the orders of a group of 10, even when he needs to interrupt his service to welcome other groups of customers before punching in his orders. However, as soon as the group leaves, it becomes difficult or even impossible for the waiter to tell who ordered what exactly. The waiter can easily keep the order in his memory for as long as it takes for his customers to be served, but by the next day, or as soon as the customers have left, he will forget.
The main hypothesis to explain this bias is that an interrupted task provokes a psychological tension, which results in a will to complete the task . This tension makes use of cognitive resources like attention and memory, which could help explain why these tasks are better remembered. Many factors can influence the intensity with which we better remember unfinished tasks, such as motivation or personality. For instance, Bluma Zeigarnik, the psychologist who discovered this bias, observed that the bias was more important in ambitious people, who forget completed tasks faster, perhaps allowing them to free cognitive resources in order to begin other tasks more efficiently. The later a task is interrupted (thus the closer to its completion), the stronger the effect.
The Zeigarnik effect has been observed in the arts, in marketing, education and elsewhere. For instance, our favorite tv series will often finish episodes with cliff-hangers, leaving the audience wanting for more, thus imprinting in memory clear details of what has just happened. In educational environments, interrupting a class in the middle of a topic contributes to enhance the memory trace of what has been discussed. This creates a motivation to know more and manifests in a better recall of what precedes the interruption . In marketing, we observe that a ‘fill in the blank’ advertising strategy is very efficient to enhance the memory of a message and, eventually, increase sales . At the individual level, it has been demonstrated that people tend to have more thoughts and regrets about situations when they prevented themselves from proceeding to action (interruption) than about situations when action was taken .
Thoughts on how to act in light of this bias
The Zeigarnik effect is generally regarded as a bias that we can profit from in order to enhance memory performance in given contexts. Researchers thus have not explicitly proposed ways to counteract this bias, as is the case with more nefarious ones.
How is this bias measured?
A classic study of the Zeigarnik effect asks participants to engage in a long series of distinct tasks (for example, stringing beads on a thread, completing a puzzle, solving a math equation). Participants are assigned to one of two groups: the first group is allowed to finish their tasks; the second group can complete only half of the tasks, and are interrupted halfway through each of the remaining tasks. Experimenters then remove all task materials from sight and ask participants to enumerate the tasks that they had to engage with. Psychologists have discovered that it is twice as likely for participants to remember interrupted tasks, as opposed to completed ones.
This bias is discussed in the scientific literature:
This bias has social or individual repercussions:
This bias is empirically demonstrated:
 Zeigarnik, Bluma (1927). Das Behalten erledigter und unerledigter Handlungen. Psychologische Forschungen, 9, 1-85. (Founding article)
 Denmark, Florence L. (2010). Zeigarnik effect, In The Corsini Encyclopedia of Psychology, Irving B. Weiner & W. Edward Craighead (Eds.). John Wiley & Sons.
 Heimbach, James T. & Jacob Jacoby (1972). The Zeigarnik effect in advertising, In SV - Proceedings of the Third Annual Conference of the Association for Consumer Research, M. Venkatesan (Ed.), Chicago: Association for Consumer Research: 746-758.
 Savitsky, Kenneth, Victoria Husted Medvec & Thomas Gilovich (1997). Remembering and regretting : The Zeigarnik effect and the cognitive availability of regrettable actions and inactions. Personnality and Social Psychology Bulletin 23(3): 248- 257.
Individual level, Availability heuristic, Need for cognitive closure
Sunk cost effect
Cloé Gratton is a PhD candidate in psychology at the Université du Québec à Montréal. She is affiliated to the Laboratoire des processus de raisonnement. She is also co-founder of Shortcuts.
Translated from French to English by Eric Muszynski.