Many of us believe that when we feel down, we should try to focus inwardly and evaluate our feelings and our situation in order to attain self-insight and find solutions that might ultimately resolve our problems and relieve unhappiness. Susan Nolen-Hoeksema, I, and others have compiled a great deal of evidence challenging this assumption. Numerous studies over the past two decades have shown that to the contrary, overthinking ushers in a host of adverse consequences: It sustains or worsens sadness, fosters negatively biased thinking, impairs a person’s ability to solve problems, saps motivation, and interferes with concentration and initiative. Moreover, although people have a strong sense that they are gaining insight into themselves and their problems during their ruminations, this is rarely the case. What they do gain is a distorted, pessimistic perspective on their lives.
Professor Sonja Lyubomirsky - The How of Happiness