‘Where good ideas come from’ by Steven Johnson 

But in fact, if you go back and look at the historical record, it turns out that a lot of important ideas have very long incubation periods — I call this the “slow hunch.” We’ve heard a lot recently about hunch and instinct and blink-like sudden moments of clarity, but in fact, a lot of great ideas linger on, sometimes for decades, in the back of people’s minds. They have a feeling that there’s an interesting problem, but they don’t quite have the tools yet to discover them. They spend all this time working on certain problems, but there’s another thing lingering there that they’re interested in, but they can’t quite solve.