Cognitive fusion is becoming so caught up in a thought that it functions like a fact, an instruction or a complete description of who you are. The term is used in acceptance and commitment therapy.
You thought, "I’m not good at this." The next sentence quietly disappeared.
The sentence that might have followed was "yet," or "without practice," or "in this particular situation."
Instead, one thought became a whole identity, and the possibility of learning left the room.
You don’t have to replace it with extravagant praise. You can notice what the thought says, what supports it and what it has persuaded you not to try.
Even an accurate thought doesn’t need to do every job. "This will be difficult" may be true. It doesn’t automatically mean "I shouldn’t do it."
Cognitive defusion explores how to create a little room around a thought. Self-image examines the descriptions that become especially convincing when they sound like who you have always been.
Russ Harris’s The Happiness Trap worksheets (PDF) offer exercises for noticing thoughts without automatically obeying them. They introduce the ACT approach from which the term comes.