You have likely experienced some form of the late-night mental loop: replaying a terse exchange with a colleague, wondering about a loved one’s subtle shift in tone, or worrying about a symptom you googled.Overthinking has become a modern buzzword blamed for wrecking everything from emotional well-being to personal relationships and professional careers.More than just “thinking hard”, it is a specific, destructive cognitive trap recognised by neuroscience. Understanding how it works is the first step to switching it off.What exactly is overthinking? Isn’t it just thinking hard about a problem?Not quite. Deep thinking is goal-oriented problem-solving. Overthinking, on the other hand, is an aimless loop driven by negative, repetitive thoughts that offer no resolution.“Overthinkers go over and over their negative thoughts and feelings, examining them, questioning them, kneading them like dough,” writes the late Yale psychologist Susan Nolen-Hoeksema in Women Who Think Too Much, a landmark book on the subject.Questions lead to more questions, she says, causing negative thoughts to multiply and spread to other areas of our lives.She says a chain of overthinking might go: “[My husband] was so quiet tonight. He must be getting tired of me. What did I do wrong? Maybe he’s having an affair. My first husband left me, too. I’m just impossible to live with.”Psychologist Susan Nolen-Hoeksema is the author of Women Who Think Too Much. Photo: hachette.com.au