Not that we need to slow down and make some kind of special accommodation when this happens -- because indeed, such episodes may fairly be viewed as signs of a lack of experience and confidence.
But it still surprises me how often people fail to see the basic humanity at play in these situations: instead of thinking "poor guy, he seemed really nervous", all that comes to mind is "What a loser! He couldn't solve that Euler problem with me staring and grinning impatiently at him the whole time. How did he ever make it through the phone screen?"