The word in French that corresponds to the English 'disappointment' is déception, a coincidence which points to the truth that every disappointment results from a deception, a self-deception to be more precise (Sarte's mauvais foi was so translated.) Disappointment is one of those peculiarly self-regarding emotions, it exists because of clash between a reality and an investment strongly freighted with the will-to-exist, with the agenda of your ramifying personal narrative, with 'self-empathy', the high-class variant of self-pity. That such emotions even arise, and they constitute the main focus of your 'psychological' life, is very strange since they dissolve into nothing when seen from the distance of a metaphysical shift. One aspect of art is to invoke the sense of such a shift without actually making it, or affirming both sides at once.