Hi, I thought you may like this Mentalrobics exercise from Braingle.com:
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Three Happy Things

Unfortunately, people often get into a pessimistic mood where they can only see the failures and problems with their life. This can cause people to experience stress [ For more on 'stress' go here: http://www.braingle.com/mind/739.html ] and its many negative side effects [ For more on 'negative side effects' go here: http://www.braingle.com/mind/566.html ].

One way to become more optimistic is to take a few minutes at the end of each day to think about the good things that happened. These don't have to be big events; it could be as simple as having a good sandwich for lunch. Record three of these happy things in a notebook, which you can review whenever you need a pick-me-up.

If you practice this exercise every day, you will get into the habit of recognizing the positive events in your life and forgetting the negatives.
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For more mind exercises: http://www.braingle.com/mind/