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How many of you assumed that this is about fitness when you read that 'Title'? Of course I'm all for you exercising your muscles through aerobic and strength training but I'm not actually about to write about those sorts of muscles.
I want to talk about those 'muscles' that you exercise when you have a success towards your weight loss goal. Here are a few examples. You're sitting in front of the television, about to settle down to a good program, and your mind wanders to the kitchen where you have a delicious packet of cookies. You're not hungry because you've not long ago finished your evening meal. It's just that those cookies somehow go together with your favorite television program. But you take control and you decide that this program will be good enough on its own; it doesn't need cookies too. You tell yourself that if you get hungry later in the evening then it will be fine to have a cookie (note 'a' cookie).
You have now exercised a 'success' muscle. Feel its strength. It feels good. Flex it. Imagine using it often. That would feel even better. Now next time you're faced with a craving, imagine your success 'muscle' and feel its power. The more you use it, the stronger it will get, just the same as your body's muscles. Use them and they'll keep you strong; neglect them and they'll weaken.
So with your 'success' muscles. They need constant use and then you'll find yourself moving towards your goal weight.