Thinking too hard hurts the brain.
A study has found that people get stressed and annoyed more quickly when making a large mental effort and warned that teachers and employers should ease off their students and workers.
Research titled 'The Unpleasantness of Thinking' analysed 170 studies involving 4,670 people across 29 countries and found that people scored higher in feelings of frustration when doing more difficult tasks.
Dr. Erik Bijleveld, lead author of the study at Radboud University in the Netherlands, explained: "In general, people really dislike mental effort.
"Managers often encourage employees to exert mental effort.
"On the surface, this seems to work well so you may be tempted to think that employees tend to enjoy thinking hard.
"Our results suggest that this conclusion would be false."
The expert said that people are willing to put in mental effort to learn a difficult job or skill but it does not make them happy.
Dr. Bijleveld said: "When people are required to exert substantial mental effort, you need to make sure to support or reward them."