In his book The Philosophy of Cognitive-Behavioural Therapy, Donald Robertson discusses the roots of unhappiness from the perspective of ancient Stoic philosophy and modern cognitive-behavioural therapy, which are similar. Robertson notes that the irrational "rules" and "assumptions" discussed in the psychological theory behind CBT is extremely similar to "the unconditional value judgments which Stoics believe are at the root of emotional distress. For the Stoic, it is the tendency to judge things as being inherently or absolutely good or bad which leads to irrational craving (epithumia) or fear (phobos), respectively. In Stoic psychology, irrational desire, or craving, which places too much value on external things and other people's opinions, is the root cause of anxiety. Believing that 'I have to' have (or avoid) something, or that other peopl 'must' behave (or not behave) in a certain way . . . is tantamount to saying that these things are of overriding importance in themselves, or absolute external values, as Stoicism would put it. "
Robertson illustrates the point by quoting Epictetus as writing, "When I see someone in a state of anxiety, I say, 'What can this man want?' Unless he wanted something or other which is not in his own power, how could he still be anxious? This is why a person who sings to the lyre feels no anxiety while he is singing by himself, but is axious when he enters the theatre, even if he has a very fine voice and plays his instrument beautifully. For he wants not only to sing well, but to gain applause, and that lies beyond his control . . ." Robertson concludes, "Anyone who anxiously demands, rather than merely preferring, that others praise him is being unphilosophical, and has failed to understand the nature of things in relation to his sphere of control. "