Overthinking usually gets treated as an unpleasant but harmless habit, an uncomfortable loop of the mind that at least means a person is being thorough. Two experiments that directly tested what rumination does to actual thinking and decision-making suggest it’s not harmless at all, it measurably makes people worse at the very things they’re trying to work out.
The clearest evidence comes from a 1995 study by Sonja Lyubomirsky and Susan Nolen-Hoeksema, published in the Journal of Personality and Social Psychology. Across three separate experiments, the researchers recruited college students who were either mildly dysphoric or not, then randomly assigned them to either ruminate, focusing inward on their feelings and problems for a set period, or to engage in a distraction task instead. Afterward, all participants were given real interpersonal problems to solve. Dysphoric participants who had been induced to ruminate generated significantly less effective solutions to these problems than dysphoric participants who had been distracted, or than participants who weren’t dysphoric to begin with. The effect wasn’t just about mood feeling worse after ruminating, it was a direct, measurable dip in the quality of real problem-solving.
A second study helps show that this same pattern extends specifically into everyday decision-making, not just problem-solving in the abstract. In a 2010 study by Annette van Randenborgh, Renate de Jong-Meyer, and Jan Hüffmeier, published in the Journal of Clinical Psychology, the researchers experimentally induced rumination in dysphoric and non-dysphoric adults, then measured how difficult participants found various decisions, how confident they felt in their eventual choices, and how long they took to decide. Rumination directly increased how difficult and effortful decisions felt, and separately lowered people’s confidence in the choices they made. The researchers traced these two effects to different underlying mechanisms: the increased difficulty was explained by heightened self-focused thinking, while the drop in confidence was explained by the negative mood rumination brought with it.
Together, these two studies suggest that overthinking doesn’t function as careful, extra-thorough deliberation, even though it often gets experienced and described that way. Lyubomirsky and Nolen-Hoeksema’s research shows that rumination produces objectively worse solutions to real problems compared with simply stepping away and returning later. Van Randenborgh and colleagues’ research shows that the same self-focused inward spiral also makes ordinary decisions feel harder and leaves people less confident once they’ve actually decided, through two separate but related pathways. Between the two, overthinking looks less like a more careful version of thinking and more like a specific process that actively works against the clarity and confidence a person is usually hoping to reach by doing it.
It’s worth being honest about what these two studies don’t establish. Lyubomirsky and Nolen-Hoeksema’s research was conducted with college students experiencing mild dysphoria, a low mood state, rather than clinical depression, so while the pattern is well-documented and consistent, it’s not certain the effect size looks identical in a clinical population or in people with no mood difficulties at all. Van Randenborgh and colleagues’ research experimentally induced rumination for a short period in a lab setting, which captures the mechanism clearly but can’t fully speak to what happens with the kind of rumination that unfolds gradually, over days or weeks, outside a controlled experiment.
Within those honest limits, the research offers a genuinely useful correction to the idea that overthinking is simply diligence with an uncomfortable feeling attached. It appears to be something more specific and more costly: a pattern that measurably produces worse solutions to real problems and leaves people less confident in the decisions they eventually make, which is a strong, evidence-based reason to interrupt it rather than trust it as a sign of being thorough.
