Years ago I was an ID student slaving away after hours in the junior design studio at Pratt Institute. The nightly soundtrack was Guns 'N Roses punctuated by various students swearing when the Dremel went too far, you over-tightened something and broke it, or gravity and a Snapple ruined your marker rendering. "I wish I had Command-Z in real life," I remember my buddy Randy saying.
If you're a CAD jockey and you screw something up, provided they haven't cut steel from your drawings yet, it's a simple matter to fix. Those of us that work with our hands building stuff know a very different experience. I can't tell you how many times I've mis-divided a fraction and cut wood too short, drilled holes in the wrong side, or spent hours assembling something before realizing I forgot to install that little part that goes right in the middle.
In woodworking, there are two kinds of mistakes—physical and mental. Mistakes of the hand fall into the first category. I jerk my chisel the wrong way and it creates a gash that can't be fixed. I angle my handsaw a half-degree off and the joint doesn't fit. These errors are unfortunate, but I've learned to tolerate them. My hands are my most loyal employees, so when they go slightly wrong, I forgive them.
Mental mistakes are harder to live with. I misread a dimension or mess up because I haven't completely thought through a process. I follow my plans (such as they are), and feel chuffed at my perfection when I've competed the task. But then I try to fit the piece and discover that I've made it backwards, or too small, or upside down.
Those of you that work with your hands have probably already come to the central conclusion of his essay, which highlights why we're willing to take the risk. Those of you that haven't, read the full essay here.