I remember with horror one technical interview I had. I was asked to complete a fairly basic problem, which I had actually just practiced a few hours before (the fact you can practice for these interviews indicates how questionable they are). As soon as the question was asked, I proceeded to start typing the answer and explaining what I was doing when suddenly my mind went blank, I struggled for nearly ten minutes to regain my confidence but by that point it was too late. The interviewer quickly ended the interview and told me to apply again after I had more programming experience, since apparently he was able to conclude the extent of my knowledge based upon my answer to a single question made during stressful circumstances.