From Contingency, irony, and solidarity (1989; pages 37-38) by Richard Rorty:

Another way of making this point is to say that the social process of literalizing a metaphor is duplicated in the fantasy life of an individual. We call something ‘fantasy’ rather than ‘poetry’ or ‘philosophy’ when it revolves around metaphors which do not catch on with other people – that is, around ways of speaking or acting which the rest of us cannot find a use for. But Freud shows us how something which seems pointless or ridiculous or vile to society can become the crucial element in the individual’s sense of who she is, her own way of tracing home the blind impress all her behavings bear. Conversely, when some private obsession produces a metaphor which we can find a use for, we speak of genius rather than eccentricity or perversity. The difference between genius and fantasy is not the difference between impresses which lock on to something universal, some antecedent reality out there in the world or deep within the self, and those which do not. Rather, it is the difference between idiosyncrasies which just happen to catch on with other people – happen because of the contingencies of some historical situation, some particular need which a given community happens to have at a given time.

To sum up, poetic, artistic, philosophical, scientific, or political progress results from the accidental coincidence of a private obsession with a public need. [emph mine] Strong poetry, commonsense morality, revolutionary morality, normal science, revolutionary science, and the sort of fantasy which is intelligible to only one person, are all, from a Freudian point of view, different ways of dealing with blind impresses – or, more precisely, ways of dealing with different blind impresses: impresses which may be unique to an individual or common to the members of some historically conditioned community.