How we change what others think, feel, believe and do
We remember better that which is unfinished or incomplete.
Russian psychologist Bluma Zeigarnik found in 1927 that waiters remembered orders only as long as the order was in the process of being served.
When we are holding things in short-term memory, we have to rehearse them otherwise they disappear, like a light going out. This requires cognitive effort, and the more things we are rehearsing the more effort. The waiter's trick is thus to keep spinning the plates of the open orders whilst letting those which are completed fall.
A similar effect also happens over a longer period as we worry about those things in which we have not achieve closure. Thus I might keep thinking about a problem at work over a whole weekend as it keeps coming back to haunt me.
To confuse people, give them lots of things to remember by starting to talk about something and then, before completing it, start some other story. After four or five of these initiations, they will be so busy trying to remember the starts of the stories they will put less attention into countering the arguments and ideas you are putting forward.
When teaching a multi-day course, give them a problem at the end of the day. By the next day they will have thought hard about it.
To remember things for examinations, do something that is incomplete, such that the ongoing thinking helps keep important facts in mind.
Zeigarnik, B.V. (1927). Über das Behalten von erledigten und unerledigten Handlungen (The Retention of Completed and Uncompleted Activities), Psychologische Forschung, 9, 1-85
Zeigarnik, B.V. (1967). On finished and unfinished tasks. In W. D. Ellis (Ed.), A sourcebook of Gestalt psychology, New York: Humanities Press