Our minds can be relentless, there are some thoughts that we cannot let go of.  Our thoughts can take us away, create a mood, influence behavior and wear us out.  One of the most liberating realizations in a Mindfulness Practice is that while thoughts are very real (we are having them), they may or may not be true.  When we can notice we are having a thought, we can intercept it, insert a pause and ask if this thought is really a fact.  Becoming aware of our thoughts lets us decide if we choose to merge with them or get lost in them.  The thought itself doesn't have power, it is what we do with it that gives it a charge, or not.  Try this practice to get to know the landscape of your thoughts.