A number of years ago, I read a (non-fiction) story about a young mathematician whose professor wrote an open problem on the board and the student went ahead and wrote down a solution after a moment of thought. The writer goes on to say something like
From that moment on, I was afraid of [this student].
I think the article mentioned that, when asked questions in class, many students would offer ideas without thought but that this particular student would think quietly before saying what was correct. Would someone know where this story can be found, probably in an article, and who the student was? I would like to say that the student was a young Grothendieck but my Google searches in that direction were fruitless.