I don't know about Grothendieck. But, Kontsevich's statement is telling:
For myself sometimes I work on one or two examples
Halmos (quoting Hilbert) captures this very well:
What mathematics is really all about is solving concrete problems. Hilbert once said (but I can't remember where) that the best way to understand a theory is to find, and then to study, a prototypal concrete example of that theory, a root example that illustrates everything that can happen. The biggest fault of many students, even good ones, is that although they might be able to spout correct statements of theorems, and remember correct proofs, they cannot give examples, construct counterexamples, and solve special problems.
I already mentioned what Halmos' stance was. What I'm more interested in is how is it possible to work without examples.
After reading Luke's interview with Scott Aaronson, I've decided to come back to an issue that's been bugging me.
Specifically, in the answer to Luke's question about object-level tactics, Scott says (under 3):
In a similar vein, there's the Halmos quote which has been heavily upvoted in the November Rationality Quotes:
Every time I see an opinion expressing a similar sentiment, I can't help but contrast it with the opinions and practices of two wildly successful (very) theoretical mathematicians:
Alexander Grothendieck
(from Allyn Jackson's account of Grothendieck's life).
Maxim Kontsevich
(from the IPMU interview).
Are they fooling themselves, or is there something to be learned? Perhaps it's possible to mention Gowers' Two Cultures in the answer.
P.S. First content post here, I would appreciate feedback.