Your mind doesn’t always mean what it says. If it tells you you’re stupid or a loser, try repeating those words and soon they will lose their meaning.
A classic ACT defusion technique is the “milk, milk, milk” exercise, first used by Titchener (1916). It consists of an exploration of all of the properties of a single word. For example “milk” is white, creamy, and so on. This word is then said out loud by the therapist and client rapidly for about a minute. In the context of rapid repetition, it quickly loses all meaning and becomes just a sound. Often the exercise is repeated with a single word variant of a core clinical concern or troublesome thought the specific client may have (e.g., mean, stupid, weak, etc.). The experiential point is that thoughts do not mean what they say they mean, and while it may not be possible or healthy to experience their referents, it is always possible to experience them as an ongoing process if the context in which they are occurring is changed.’
Steven C. Hayes. Acceptance and Commitment Therapy, Relational Frame Theory, and the Third Wave of Behavioral and Cognitive Therapies in Behavior Therapy (2004).