I'm going by memory of Spolsky's article, from when I read it many years ago. One of his main points was that in asking a person to reverse a linked list, he watched to see if the person first sketched out a diagram, or simply started writing code -- because, as he believed, no one could do this without first sketching out a diagram, and going right to code was a red flag, indicating someone who (my memory is foggier, here) lacked the right temperament for a developer.