The Cognitive Distortion Behind Most Diet Failures All-or-nothing thinking is a recognised cognitive distortion — a systematic error in reasoning — identified in cognitive behavioural therapy. In its dietary form, it manifests as the belief that eating anything outside the programme is equivalent to having failed the programme entirely. One biscuit becomes a reason to eat the whole packet. One missed training session becomes justification for skipping the rest of the week. One bad meal triggers the mental accounting where the day is already "ruined" and the next opportunity for redemption …