I'm asked to perform or sit in during many technical interviews. We ask logic questions and simple programming problems that the interviewee is expected to be able to solve on paper. (I would rather they have access to a keyboard, but that is a problem for another time.) Sometimes I sense that people do know how to approach a problem, but they are hung up by nervousness or some second-guessing of the question (they aren't intended to be trick questions).

I've never heard my boss give any help or hints. He just thanks the interviewee for the response (no matter how good or bad it is) and moves on to the next question or problem. But I know something about the rabbit hole that defeat and nerves can lead you down, and how it disables your mind, and I can't help wondering if providing a little help now and then would ultimately help us end up with more capable programmers instead of more failed interviews.

Should I provide hints and assistance for befuddled interviewees (and if so, how far should I go while still being fair to the more prepared candidates)?

When I was in a similar position, I would say to the interviewee: "Pretend I'm Google. If you need to search for something just say so."

In one question interviewees needed to be able to figure out the volume of a cylinder, so I didn't mind if someone said, "I'd have to Google for the formula for the volume of a cylinder." I was interested in knowing if they knew how to attack the problem, not if they'd memorized formulas. For the job, they had to have a decent grasp of how to translate the real world into software, so it was an important concept.

On the other hand I wasn't going to tell them they needed that formula.

You are correct that nerves can be a problem, but I still expect people to be able to express their thought process, even if they're nervous. Simply not giving an answer was unacceptable.
