Cognitive Behavior Therapy (CBT) is based on the idea that how we think (cognition), how we feel (emotion) and how we act (behavior) all interact together. Specifically, our thoughts determine our feelings and our behavior. 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 mood, making the person feel depressed; the problem may be worsened if the individual reacts by avoiding activities. As a result, a successful experience becomes more unlikely, which reinforces the 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 directed at working together to change this. This is done by addressing the way the client thinks in response to similar situations and by developing more flexible thought patterns, along with reducing the avoidance of activities. If, as a result, the client escapes the negative thought pattern, the feelings of depression may be relieved. The client may then become more active, succeed more often, and further reduce feelings of depression.