Intuition:

"Many famous scientists have identified stages of problem-solving; these nearly always include a central stage during which unconscious cerebration, mentation, or whatever predominates. Thus Helmholtz (1896) postulated an initial investigatory stage, during which he became saturated with the large body of relevant facts. This was followed by a stage of rest and recovery, during which he gave no conscious attention to the problem, and finally a stage of illumination, when he had sudden insight into the solution - the 'aha!' experience."

Genius - H. J. Eysenck