Ideas are networks of other ideas—bricolage.

[Ideas] are, almost inevitably, networks of other ideas. We take the ideas we've inherited or stumbled across, and we jigger them together into some new shape. We like to think of our ideas as a $40,000 incubator, shipped direct from the factory, but in reality they've been cobbled together with spare parts that happened to be sitting in the garage. 

— Steven Johnson

An ah-ha moment feels like it came out of no where. In reality, your brain bricolages together "the spare parts that happened to be sitting in the garage". These are things you've heard, read, seen, experienced. Your knowledge base. Associations are made and then 💥 :

Combinatory creativity.