Cognitive-behavioural psychologists encourage clients to not believe everything they think. One way to apply this suggestion is to imagine your mind as an email inbox and some of your thoughts as spam. In the same way that you don't take seriously every email informing you that you've just won £20,000,000, maybe you don't need to take seriously every thought that runs through your mind.
When you believe everything you think and react to your thoughts as though they were facts, you're experiencing what psychologists call cognitive fusion. Say I have a tough session with a client and I have the thought "I'm a bad therapist." If my heart sinks and a knot of shame forms in my belly, I'm fused with my thought--that is, I'm reacting as if the thought were a fact, rather than a mere string of words my mind created. What's problematic about fusion is that we can get so wrapped up in a fused thought that we fail to notice or incorporate any information that disconfirms it. For example, say a depressed client were fused with the thought "Life is hell." Cognitive fusion would maintain his grey-coloured glasses and prevent him from noticing anything pleasant about the world around him.
Cognitive defusion is used in psychotherapy to help clients unhook from painful and stressful thoughts. A lot of defusion techniques involve using mindfulness to see thoughts and emotions as transient external events, observing them in the same way you would observe a bus drive by or a pen fall to the floor. You might picture your thoughts like leaves on a stream, each one just floating into and then out of consciousness, or you might add the words I'm having the thought that to the beginning of your sentence, so that instead of saying to yourself "I'm an idiot," you would say "I'm having the thought that I'm an idiot." In so doing, you acknowledge that your thought is just a thought, not a fact.
Other defusion methods include saying the fused thought out loud over and over until it loses meaning, saying it in a silly voice, and singing it. I went to a conference a couple weeks ago where I attended a workshop on cognitive defusion techniques; the presenter showed us an iPhone application called Songify that he uses to help his clients defuse from thoughts. The app records you speaking, analyzes your speech, organizes it into a chorus and verses, and maps it to your choice of melody, adjusting your pitch and syncing your words with the beat. He played us a demo of a client saying "I'm a loser." It was impossible not to laugh at the electronic but melodic "I'm a loser" song and it really made the words seem like just words. Apparently the client felt the same way.
I tried Songify recently with colleague, testing some of the thoughts we sometimes find ourselves fused with. It worked! Not only did we have a good laugh, but hearing our thoughts sung out loud to a melody gave us some distance from them, letting us see them for exactly what they are--mind spam, rather than literal truths.