It is an entertaining article, but I am not too sure if I agree that Knuth was yak shaving. However by luck, inspiration, conviction or observation he understood what makes a program last. You focus on one thing and you do it well. On the way you resolve all the problems. He famously said that at first he had one user: himself but then things were different when he had 1000 users. At that stage you need to remove bugs and hence his famous checks rewarding people that reported bugs. When your user base grows allow them to extend the program through their own code. I also think that the program adapted well, throughout the four decades of its usage due to the well thought level of abstraction. Nearing my three score and ten years, and using TeX/LaTeX for all these decades, I can with confidence state, that the only people yak shaving was us all the early adopters, learning typography rather than focusing on our studies. The same can of course be said for current users.
I understand what you mean with this in context, and it's true, but it's still somewhat funny to talk about Donald Knuth and "focusing on one thing". It's more like he focused on everything in programming, and somehow does it well.
I'm not sure that it's slow moving. It's just that it generally grows on the edges, and unless you're out near the edges, you've no idea how quickly the edges are growing.
Fair enough, my view of mathematics is very much the lay persons field, seeing the mainstream mathematics as mostly unchanged for the last decade or two, but for someone doing mathematics professionally in a research capacity I would expect them to see nothing but green fields and novel approaches. And as the field grows (assuming a two dimensional, spherical math field here for the moment) so do the edges.
As someone only on their two score and ten, (and many bald yaks behind me) do you have advice for keeping on writing code as opposed to the horrors of management ?
Stay out of the hierarchy and start consulting, specifically troubleshooting. The rates are higher because the clients need to get stuff done and a lot of red tape will be cut for you by people in a position to make decisions. Also: your customers will be genuinely happy. Then: leave. Don't hang around because you'll become part of the problem, no matter how much they offer.
Increase your price by 25% every year or so, until you start losing customers, and ask your previous customers if you can use them as a reference.
It's a good gig because it actually requires something that is somewhat rare: lots of experience, so it's a natural match for the older hands-on tech people.
