Incubation. https://en.wikipedia.org/wiki/Incubation_(psychology)

> In psychology, incubation refers to the unconscious processing of problems, when they are set aside for a period of time, that may lead to insights. It was originally proposed by Graham Wallas in 1926 as one of his four stages of the creative process: preparation, incubation, illumination, and verification.

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> The experience of leaving a problem for a period of time and then finding that the difficulty evaporates on returning to the problem, or, even more striking, that the solution "comes out of the blue" when thinking about something else, is widespread. Many guides to effective thinking and problem solving advise the reader to set problems aside for a time.