[lisper]

Actually, under non-brain-wedgie conditions, I can re-derive Newton-Raphson because I do have a good conceptual grasp of it. (In fact, after I got off the phone, I did it just to convince myself that I could. It took me about five minutes, which is nothing under realistic conditions, but a long time when you're on the phone.) But at the time I had a brain wedgie, and the interviewer just kept pushing and prodding and wouldn't let it go. It was damned annoying. I was sitting there thinking, why are you so fixated on this?

It was definitely their loss because the technical problems they were facing were very similar to ones that I had faced (and solved!) in a previous startup (network optimization problems). But I never even got to talk about that.

Because of that experience, I now make it point whenever I interview someone to always ask, particularly if they're floundering, "What should I ask you about that will let you show off your strengths?" I don't have any qualms rejecting someone who can't answer that question (and a surprising number of candidates can't).