We like to finish what we have started. When we leave things incomplete (e.g., a puzzle), we tend to feel bad about it. This is the so-called Zeigarnik Effect.
There is one important condition to the Zeigarnick Effect. The task needs to be interesting so that we are motivated to complete it. If we find the task unattractive due to its degree of difficulty, the Zeigarnik Effect does not occur. So the goal must not be too difficult to reach because then we do not bother to reach it.
A number of studies have supported the idea of the Zeigarnik Effect. In one study (McGraw et al., 1982), participants were told to solve a difficult puzzle, but they were interrupted before they completed it. After they had been interrupted for a while, about 90% of the participants carried on working on the puzzle, even though they were not told to do so.
According to Greist-Bousquet & Schiffman (1992), people have a need to complete a task once it has been started. A need for closure. In their study, one group of participants was asked to solve a list of 10 three letter anagrams. Another group was asked to solve a list of 20 three letter anagrams.
The second group was interrupted after they had completed the first 10 three letter anagrams. They knew that they still had 10 more to complete, i.e. they felt frustrated because they could not return to their tasks.
The two groups were then asked to estimate the amount of time it took them to solve the anagrams. The first group did an estimate that was very close to the actual time it took them. The second group’s estimate, however, was not as accurate.
They markedly overestimated the amount of time it took them to finish. The authors suggest that the participants overestimated because they were interrupted.
The interruption simply resulted in feelings of frustration and distress as a result of the Zeigarnik Effect. These feelings then influenced the group’s estimates.
In closing, your mind will tell you that you need to get things done, if the goals are attractive and possible. Once you have begun, you are very likely to finish. But if you begin with tasks that are way too difficult, it is also more difficult to stay motivated.