"Don't believe everything you think" is a 🏷️#principle drawn from cognitive-distortion psychology and mindfulness-tradition writing — the observation that the experience of having a thought does not establish that the thought is true or load-bearing for action.
Variants of the phrase appear on bumper stickers, in self-help, and on the title page of Joseph Nguyen's 2022 bestseller of the same name. The underlying move is older and broader: cognitive behavioral therapy formalizes it under "cognitive defusion," asking the thinker to notice a thought as a thought rather than identify with its content. Buddhist and Stoic traditions arrive at adjacent conclusions through different routes.
As a working heuristic, it cuts across rumination, anxiety, and reactive decision-making — the friction of pausing between thought and identification is itself often the entire intervention.