The primary way in which interviews are different from after-the-hire social interactions is that interviews are high-stakes events,
and the candidates know it. For some people, that knowledge is enough to put them into a self-reinforcing mental death spiral. Their fight-or-flight response takes over and they literally stop thinking as their bodies switch into survival mode.
That's why, when you're interviewing candidates, your first job is to get them to relax. Start out with small talk and softball questions until you sense them unwind. Then move slowly into the real questions.
When you get to the coding problems, again, start with dead-simple questions so that the candidates have the time to gain some confidence before the harder problems arrive.
The first programming problem I give – and this is after some small talk – is usually something like, "Print the odd integers between 1 and 100, in increasing order." This problem is so simple that it doesn't tell me anything about the candidate's ability, but that's okay. It helps to calm the candidates so that when I get to the problems I care about, I'll get better measurements.
That's the goal: To measure how the candidates actually perform, not to see whether they'll choke under interview stress.
