Concepts which have proved useful for ordering things easily assume so great an authority over us, that we forget their terrestrial origin and accept them as unalterable facts. They then become labeled as 'conceptual necessities,' etc. The road of scientific progress is frequently blocked for long periods by such errors.
Each thing leapfrogs. I do a Genesis project - like now, we're just finishing off an album - and then by the time the album is doing its thing, I could do nothing or I could do a film.