I saw a Yoplait ad on tv that illustrates two of the most common traps dieters fall into -- and all in the first nine seconds!

Watch it for yourself below, then read on to learn more about what the mistakes are:

1. Moral Licensing. Do you use past good behavior to justify indulging? As in, I ate a healthy breakfast -- so it's OK if I eat a fast food lunch? Or, I exercised today -- I deserve a treat! Psychologists know that moral licensing is rarely logical -- we give ourselves permission to indulge in ways that completely undo our hard work. But as long as you define goal-consistent behavior as "being good," you'll feel the pull -- and the right -- to be "bad." It's far better to keep your eye on the prize, and view making healthy choices as cumulative -- the more positive choices you make, the closer you are to your goal.

2. The Halo Effect. Studies show that when a cheeseburger is paired with a green salad, diners estimate that the meal has fewer calories than the same cheeseburger served by itself. This makes no sense, unless you believe that putting lettuce on a plate can magically make calories disappear. What's really happening? The salad gives diners the feeling that the meal they’re eating is virtuous. Those lettuce leaves come with a health halo that casts a glow on the burger, making it more likely they will underestimate the health “cost” of the meal. Dieters—who in theory, should be most likely to know the calorie counts of foods—are the MOST susceptible to the halo effect, taking 100 calories off their estimates when a salad was added. When it comes to food choices, don't be blinded by a side vegetable, the label "organic," or anything else that might make vice look a little more virtuous.

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