Can we change our defining characteristic, and the answer to that is yes. As a whole or a group after a certain amount of time, you will naturally gain or lose characteristics, naturally become more conscious, more emotionally stable, etc. (as we age) As part of psychotherapist studies, they must have a theory of personality, of how people work, fi your going to have an idea of how and what depresses them. Series of personality change are based on a more basic theory of personality. One very prominent theory of change mechanisms is freudian psychoanalysis. Early childhood is important, the ideas of conflict, anxiety, all of freud"s ideas. Wide range of defence mechanisms to protect ourselves from anxiety, but they don"t always work, cannot withstand magnitude of anxiety. And how at each stage, particular component of personality comes online. Our impulse is to return to a more happier, safer time, when things were still unresolved, earlier stages.