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Your brain is telling you she's hot and available, but your gut is urging you to zip up and run. Which will it be? You can, in fact, trust your gut with the big choices, but your rational mind has its strengths as well. This handy chart shows exactly when your heart or your mind should have the upper hand.

You should go with your gut when you're...

...MAKING A MORAL DECISION

Why: If you're good friends with a married couple and one of them is having an affair, do you tell the other spouse? "Moral judgments are a combination of intuitive gut reactions and reflection. Without your gut, you'd make arbitrary decisions," says Fiery Cushman, Ph.D. (c), a researcher at Harvard University.

The strategy: When faced with a moral conundrum, weigh the practical facts but heed your inner monologue for the right decision. (Discover the trick to making better decisions.)

...SECOND GUESSING YOUR DOCTOR

Why: Doctors often overlook symptoms that don't fit with the usual model of a disease and often dismiss fears as paranoia, especially in healthy young men, says John Amory, M.D., an associate professor of medicine at the University of Washington.

The strategy: You're the only person who can "listen" to your body. If it's telling you something's lurking, Dr. Amory recommends finding a specialist outside your primary doctor's group. It just may save your life.

...PLAYING A GAME

Why: In a Michigan State University study, expert chess players performed as well in "blitz chess" (a 5-minute version of chess) as they did in the traditional game. The takeaway: Overanalyzing won't improve your performance.

The strategy: On a test or in a game, the choice that feels right is often correct, says Paul Slovic, Ph.D., president of Decision Research, a nonprofit group that studies human judgment and risk analysis. "That feeling you have is your intuition checking up on your analytic thinking." (Learn when should you trust your instincts.)


You should go with your brain when you're...

...HIRING A JOB CANDIDATE

Why: If the potential hire is agreeable and funny, your instincts are wired to choose him over an aloof candidate who's more qualified, says David Myers, Ph.D., author of Intuition.

The strategy: You can't completely avoid your impression bias, but you can control it with structured interviews. Set questions and scaled ratings are three times better at predicting on-the-job success than informal talks, according to a study in Psychological Bulletin.

...INVESTING

Why: When it comes to money, your gut is often influenced by the herd mentality, says Myers. Take equity funds backed by subprime loans. By definition, these are investments in borrowers who are poor risks, yet plenty of people raced to buy in — and now they're paying for it.

The strategy: Reason and analysis should guide most of your investing, leaving only a small window for hunches (economists agree some intuition is wise). But ignore the frenzied pack — and all things subprime. (Get more cool life tips like these delivered straight to your inbox when you sign up for our FREE Daily Dose newsletter!)

...JUDGING HER SINCERITY

Why: You want to believe her when she says she'll never cheat on you again. But studies show that past performance is the best predictor of future behavior, despite what your gut is telling you.

The strategy: When a flaky friend asks for yet another loan or your girlfriend says she's finished catting around, pack up and walk away. Your intuition to trust them in the past was faulty, so fight your gut and don't repeat the mistake, says Gary Klein, Ph.D., author of The Power of Intuition.