Innovation rarely occurs as a Eureka moment. Instead, it happens through a series of incremental steps. This evolution is constrained by what came before. We can imagine this evolution as a room with many doors. You can choose the door you walk through, but the room constrains which other rooms you can enter. This set of doors is the adjacent possible.
If you’re not bold enough, it’s already been done. Too bold and you’re ahead of your time. The Adjacent Possible model nicely explains why important discoveries are often arrived at simultaneously by multiple discovers in different places.
This is closely related to the idea of Zone of Proximal Development in learning and education. I first read the idea in Where Good Ideas Come From by Steven Johnson, attributed to Stuart Kauffmann. It's also very related to the Seek interesting stepping stones idea from Why Greatness Cannot Be Planned by Kenneth O. Stanley.