Making assumptions is a necessary part of diagnosing mechanical problems, and of living life in general. But like most things, there are good and bad assumptions. Good assumptions based on empirical evidence, factual information, experience and knowledge can be quite helpful. But bad assumptions, as Robert Pirsig reminds us in Zen and the Art of Motorcycle Maintenance, are traps to be avoided as they can mislead, direct you down dead-ends, and greatly complicate the task at hand.