Terence Tao's obit: "Thurston was also an amazing mathematical expositor, having the rare knack of being able to describe the process of mathematical thinking in addition to the results of that process and the intuition underlying it. His wonderful essay, which I highly recommend, is the quintessential instance of this." \\ Non-technical discussion of progress (and polite fiction :-) in mathematics that are not captured by formal proofs of theorems, especially in Thurston.own work -- presented with unusual frankness and clarity about the "personal understanding" beyond knowledge of mathematics. [Animated GIF illustrates the Poincaré disk as a model for hyperbolic geometry.] - Adriano

"I think that mathematics is one of the most intellectually gratifying of human activities. Because we have a high standard for clear and convincing thinking and because we place a high value on listening to and trying to understand each other, we don’t engage in interminable arguments and endless redoing of our mathematics. We are prepared to be convinced by others. Intellectually, mathematics moves very quickly." -- ibid. - Amira