Positive thoughts and emotions

Hi! I really love the model and seem to believe that we must be fueled with positive thoughts and emotions to create a positive results. However I am encountering a lot of situations when people think highly about themselves, talk about themselves as being positive and amazing but do not show up like that. Does it mean that they are not believing these statements or rather lying to themselves? E.g. my younger sister has a very high opinion of herself (at least expresses such opinion out loud) but I see that she treats her body terribly with diets and over drinking. Does it mean that she does not actually believe this positive opinion about herself ? Any help is highly appreciated !