A characteristic unique to humans is the amount of time we spend thinking about what isn't happening: the past, the future, or hypothetical situations. This type of thinking, known as mental wanderingMindfulness is considered a key capacity for learning, reasoning, and planning, but various philosophical and religious traditions suggest it can have an emotional cost. Based on this hypothesis, a team from Harvard University analyzed the relationship between mind wandering and emotional well-being in everyday life. Using a mobile app, the researchers, led by MA Killingsworth, collected real-time data from more than two thousand adults, who reported what they were doing, what they were thinking, and how they felt at that moment. The results showed that the mind wanders almost half the time, with little variation depending on the activity, and that happiness levels are lower when thoughts are not focused on the present activity. In other words, when it comes to explaining emotional well-being, what we think about is more decisive than what we are doing, and that a wandering mind, despite its cognitive value, carries a measurable emotional cost.