In this chapter I categorize and describe my many mistakes. I begin by describing and exemplifying what I call dope-slap mistakes, embarrassing errors that even someone walking into the shop from off the street would likely have avoided. I follow up with communication mistakes, gaffs brought on by both written and spoken miscommunications. Perception mistakes, I argue, stem from an insufficient ability to perceive with expert senses, such as failing to recognize a weld defect. Knowledge-of-what mistakes arise from insufficient conceptual knowledge, such as my lack of knowledge about tungsten size and the ways it impacts tig welding. Knowledge-of-how mistakes, on the other hand, relate to procedural knowledge—how to do something. My days at Howe’s would overflow with such mistakes if I did not have recourse to Jim and my more-expert coworkers.