Spencer Lewis of Insider Carpentry has gained a big following on social media thanks to his meticulous carpentry skills and low-key video presentations. But on this project - a complicated set of stairs that Lewis prefabricated in sections in his shop - he made a layout and measuring error that only became apparent when he lowered (with the help of a powered winch, which is reason enough to watch the video, by the way) one of the sections into place. As Lewis explains, it's not the mistake that's important, though, because mistakes always happen on a jobsite; it's the skill and thought process that a carpenter uses to fix the problem.