Software engineering Question:

On more than one occasion, when I gave a star candidate a coding question, he zeroed in on the most optimally performant solution, identified the boundary cases, and began writing well-designed code. Midway through the problem, he makes a little error -- getting the order of operations wrong on the first try, or having an off-by-1 error, or forgetting to declare a variable.

When I point it out, the candidate responds with horror and then becomes so nervous that it impacts his performance during the rest of the interview.

The fear is unfounded. An awesome candidate making a little error is like a concert violinist playing a challenging Brahms concerto and hitting two wrong notes. Sure, the audience could tell that he made mistakes, but they don't get confused as to whether he's actually at Twinkle-Twinkle-Little-Star level.

Even if you completely bomb one question, many interviewers ask you multiple questions and will forgive a single mishap. Even bombing an entire interview is recoverable if the other interviews go well.