There's basically only one thing I've so far done in my life that I do regularly and keep in practice doing, for about 40 of my 48 years: knife sharpening. I'm at the point of mastery, now. I can usually get a knife razor or near razor within 5 minutes or so, assuming it ever had an edge, using a combination of surfaces like rocks or the bottoms of ceramic bowls and plates. If I have my sharpening stones and other supplies, maybe 2 minutes.

I feel like if I were that good at development (I'm not - I've done development on and off throughout my life, but only been paid to do it maybe 5 or 6 years out of the more than 20 I've been in IT), I would be able to roll my own library in any language without really thinking about it. I know or have programmed in a shitload of languages, starting with BASIC and 6510 assembly, and going out to MongoDB and golang, but never really stuck with one for ver long.