Meta-analysis: Thinking hard feels bad. apa.org/pubs/journals/releas… This meta-analysis provides a new, central piece of evidence for models that assume that mental effort is costly. The main finding from this meta-analysis is that mental effort is strongly associated with negative affect. We found this association in all types of tasks that we studied, including tasks that have motivating features (e.g., tasks in which people have autonomy, tasks in which people receive feedback, and tasks in which performance has real world consequences). Furthermore, we found this association in all types of populations that we studied, including populations in which mental effort likely had been rewarded in the past (e.g., experienced professionals, university-educated people). Thus, our findings showed that when a sample of participants felt more effort on average, that sample also tended to feel more negative affect on average. Finally, it is important to note that people may justify their effort expenditure after the fact. That is, when people do something unpleasant to attain some goal (e.g., exert effort, endure pain, undergo humiliation), they may later infer that that goal must have been very valuable to them. After all, why else would they have carried out the aversive action? This notion of effort justification [is related to] the so-called Ikea effect.