I have a long record of walking out of interviews certain that I have found an action man. He answers fast, he talks about the floor, and he has an opinion about why the shift change happens at the wrong hour which he offers before I ask for it, so I hire him.
Three months later I discover he is a thinker. He can explain the process beautifully. He can tell me where it breaks and why it breaks, in detail, at length, with a diagram if I am unlucky that day. Asking him to walk over and fix it produces a fresh explanation.
There is nothing wrong with the man. I have made this mistake often enough now that I have stopped blaming the candidates for it. The mistake is mine and it begins before he sits down, with the two boxes already drawn in my head. Thinkers on one side, doers on the other, and forty minutes to decide which one is sitting across the table from me. Every plant, every family business and every interview room I have been in runs on those two boxes.
Bhagwad Gita 5.4 says that only children speak of sankhya and yoga as separate paths, and that a man properly established in either one arrives at the fruit of both.
Krishna is being strict here. The word carrying the weight is samyag, properly, all the way. Which means the man I hired was never a category problem for me to solve. If he could analyse the line and could not repair it, he had simply not gone far enough into the analysis to reach the repair. A man properly established in understanding a machine ends up with oil on his hands. A man properly established in fixing machines ends up holding a theory. My two boxes exist only in the shallow end of the pool, which is where I have spent most of my interviewing life.
So I have changed the question. I ask how far someone has gone into whichever one he claims, and then I keep asking, and the place where his answers run out is the real information. Depth is harder to perform for forty minutes than confidence is.
My suspicion now is that most of my bad hires were depth errors wearing the costume of category errors. If someone has found a reliable way to test for depth inside a single interview, I am listening.