On weekends, some people watch TV series, others go on walks or play sports, while many choose to read serious books on personal development or management. In general, people often imagine that smart individuals spend their free time reading "useful" books filled with practical advice and theories that can be applied at work. However, those who spend their days thinking often use their weekends to read novels, getting lost in stories without taking notes or looking for explicit lessons. What might seem like the least profitable leisure activity is actually one of the most powerful mental exercises. Most people who want to "become more intelligent" tend to read non-fiction, such as economic essays, business books, and guides on how to organize themselves better. This choice gives the impression of being responsible, almost virtuous. By the end of the weekend, one can summarize what was learned and feel that time was well spent. Reading fiction, on the other hand, appears to be a lighter option, something people do when they are too tired for "real" books. "People who make a living by thinking spend an entire Saturday afternoon immersed in a novel, without taking notes, and derive nothing they can summarize at work on Monday," says psychologist Mark Travers for Forbes. This seems to be the least productive activity on their agenda. Yet, it may be more beneficial to their thinking than the books they are proud to have finished. To explain these seemingly unproductive hours, cognitive scientist Keith Oatley compares fiction to a flight simulator. A novel allows one to spend time in the mind of another without the risks of a real error. Researchers refer to "theory of mind" to describe this ability to guess what someone thinks or desires. By following several characters at once, the reader keeps track of what each knows or doesn't know and what they perceive. This mental exercise doesn't remain confined to the pages of the book. In daily life, it helps understand that a colleague accepted a decision against their will or that a friend who replies "it's fine" actually hopes to be contacted again. Reading fiction requires holding several perspectives in parallel for a long time: that of the character, that of the others around them, and that of the reader who sometimes sees what none of them have yet perceived. Few common activities require such careful tracking of others' mental states. Recent research highlights another mechanism, less visible but central. Psychologists describe a trait called "cognitive closure need": the discomfort with ambiguity and the tendency to adopt a reassuring explanation quickly. A study published in Scientific Reports shows that people highly elevated on this trait mainly seek individuals who think like them and distance themselves from discordant voices, especially when the environment is uncertain. Non-fiction reduces uncertainty by presenting a thesis and then proving it. Fiction, on the other hand, maintains shadowy areas and open endings, and trains one to stay curious when not everything is understood yet. Whether it is a classic novel or a psychological thriller, in paper or audiobook form, the essential thing is to let oneself be carried by the story rather than trying to profit from the reading. This apparently useless time can deeply transform the way one thinks about others and complex situations.