I thought that, too, after the recent interview I described in my comment on the OP. When did I ever need to think this hard? Um, when I was writing proofs in my Semantics of Programming Languages course at university, I guess. Most of my work days are spent pondering gently, with - a few times each year - a trip to the library to hunker down and really crunch some x's and y's. But it did make me wonder whether I wasn't choosing sufficiently challenging work, in the sense of the amount of raw "think, think, think" effort required.