Oh, Robert Langlands! I worked on a short film about him, for the Abel Prize ceremony, last March. http://www.abelprize.no/artikkel/vis.html?tid=73176
I like the part where he said he began to write before he understood everything, and in order to write he had to discover many things, and even had to discover them after he started to write.
It underscores the crucial role of writing in discovery. Most writers will tell you they are exploring the space during the writing process. Writing isn't a process of committing what you already know to paper; it's a process of learning what you don't know and or haven't considered. It often leads you down paths you would never expect. (this happens to me with my HN comments too -- I often myself writing a very different comment from the one I set out to write)
This is why I think a Ph.D. dissertation should be a continuously evolving collection of notes, and not something you "write-up" in the end after all the work is ostensibly done.