German therapist Hermann Ebbinghaus identified distinct patterns of memory and forgetting from the results of his experiments. As well as rapid onset and slow decline that marks what he called the forgetting curve, he noticed a similar “earning curve” associated with memorizing.
When we learn a list of things, for instance, we tend to remember the items at the beginning and the end, better than those in the middle of the list.
The Russian psychologist Bluma Zeigarnik later discovered another distinctive feature of memory, when watching waiters in her local cafe. If asked about what someone had ordered, they could remember the order exactly if it had not yet been paid for, but found it much more difficult to recall once the check had been settled.
Memory of a completed transaction was no longer important and was “put to one side” to make room for new orders. In later experiments, Zeigarnik found that an unfinished or interrupted task tends to be better remembered than one that has been completed.