Cognitive Behaviour Therapy (CBT) is based on the idea that how we think (cognition), how we feel (emotion), and how we act (behaviour) all interact together. Specifically, our thoughts determine our feelings and our behaviour. Therefore negative thoughts can cause us distress and result in problems.

One example could be someone who, after making a mistake, thinks "I'm useless and can't do anything right." This impacts negatively on their mood and makes them feel depressed; then they worsen the problem by reacting to avoid activities. As a result they reduce their chance of successful experience, which reinforces their original thought of being "useless".

In therapy the latter example could be identified as a self-fulfilling prophecy or "problem cycle", and the efforts of the therapist and client would be to work together to change this. This is done by addressing the way the client thinks in response to similar situations and by helping them think more flexibly, along with reducing their avoidance of activities. If as a result they escape the negative thought pattern, they will already feel less depressed. They may hopefully also then become more active, succeed more, and further reduce their depression.