In Sufficient condition of creativity, I show that hard work can be called "creativity". Continuously improving designs until the working version is unrecognizable from it starting version. This is based on the Darwinian evolution concept.
Most Science advanced in the Darwinian way, paintakingly testing and disproving theories until an elegant new theory appears.
Other type of "great leap forward" is made when a sudden connection between two theories are connected and sparks off an insight. [see e.g. Brain Scans Show Working Memory, Moments Of Insight] This is the Eureka Moment - after the myth that Archimedes, fresh from discovering the principle of buoyancy during a bath, running naked through the streets of Syracuse yelling “Eureka!”
Since such Eureka Moment requires connection between previously considered unrelated theories, the necessary condition of Eureka Moment is the board scope of the creator. Without knowledge of the two theories, there could not be any connection. This again points to "diligence" as an important factor. In this case, a potential creator should read/understand a board scope of theories. When the spark lights, Aha! Eureka!