I agree that intuition and thinking often precede speaking and writing. However writing is a great tool to clarify and elaborate our thoughts. The point is not to be a talented writer but to take the most of our ideas, to make them stronger before we can convey them to others and this can be done using a different medium.
The fact that you don't see a need to offer any justification for that statement ... proves PG's point.
It proves, perhaps, that writing is important to communicate and persuade others of your thoughts. But some people already know the truth i’m pointing at. I don’t need to justify it to those who know, and didn’t intend to convince those who dont - so i understand if you are not convinced ;)