The hardest thing for me to do is to make more than one of anything. I learned this, and an important concept, many years ago.
At the time, I was doing a lot of leather work and one day it occurred to me that I should make a pair of moccasins. Early on, when I got an idea, I'd be in the shop within minutes, diving headlong into the project. Later I realized that it might be better to let the idea bounce around in my head for a bit. But that's another story.
Since I was in my "headlong period", I went right to work. I had little idea about how to go about making a shoe but I knew enough about working with leather to produce something that at least resembled a moccasin. And it wasn't bad for my first try. The only problem was, I needed two. While the second one did in fact closely resemble the first, they were nowhere near identical. Even so, a close friend liked them enough, dubbing then Indian Football Shoes, and wore them.
That was when I discovered the concept of batch processing, a contemporary term applied mostly to CNC work. The concept applies to any situation in which multiple items are needed. Success is much more likely if the parts are processed together rather than sequentially. This might seem obvious but it's amazing how many of these simple concepts need to be learned by each of us as we move through life.