I once learned a shocking lesson about the influence of my preconceptions when I accidentally took a developer through three rounds of interviews because he previously worked for Pivotal Labs and had a German (aka technical) accent.

It wasn't until the third interview that I asked him to write an algorithm to sort an array and when he couldn't I suggested instead writing an algorithm to see whether the array was already sorted. When he couldn't do that either he told me I was asking the wrong questions and not letting him show off the code he was good at.

To this day I have wondered and never discovered what type of code doesn't involve arrays, loops and comparisons however I do now ask candidates to write code right at the start of the interview loop. I simply never anticipated how many non-programmers would apply for programming positions.