In CBT groups we work on catching the lies we tell ourselves (I can't stand it; they don't like me; I'll never meet my goal). We try to figure out what kind of lie we're telling ourselves. Are we blowing things out of proportion, are we mind-reading what we imagine others think about us, or having thoughts that are fatalistic? Once we have identified how we're not being accurate or truthful in our thoughts, we work on coming up with a more positive, or more accurately, a more realistic thought.
In a New York Times article yesterday, a psychologist writes about why it is important to have realistic thoughts when thinking about goal attainment. It's a quick article. Great read.