Explain. If you can't produce a god damned string reversal function in 10 minutes, why would I believe you can produce a bug fix to your own, complex code in a few hours? That's what interviewers are considering: the interview is a proxy to see if you can come close to the requirements of the job.
I can program a string reversal with my eyes closed, tied up in chains, upside-down, while holding my breath. Or whatever.
The point is more that for a person with a given skill level, interviews can be stressful and make them perform below that skill level. I try to structure my interviews such that people get more comfortable and I don't ram their head into a metaphorical wall. I get all the same information, but without all those hard feelings.
Can you get in the zone with people watching and judging you intently? If you can't get into the zone with only a couple of people watching you, how will you get into the zone when the whole company is depending on your bug fix?
The pressure of judgement is not the same as the work pressure of a stressful scenario. It's why public speaking and job interviews are among the most feared activities people go through, but people consider meetings boring and mundane.
Easy, the company that is depending on me is not physically there, watching and judging me. Sure they probably are watching and judging me, but as long they're not physically present that makes all the difference to my mind...
