Man, that's a crazy amount of work. I mean, I messed up my elbow pretty bad a few years back just from too much sanding on some furniture projects. Had to wear a brace for like a month, and it totally changed how I plan my shop time now. Maybe it's just me, but I try to mix in totally different motions, like sweeping up or organizing, to break up the repetitive stuff. Still feels like a losing battle sometimes though.

Oh man, pre-mixed stuff is the worst for that. It doesn't set up fast enough on a vertical surface. You need the powder kind you mix yourself, the thinset. That stuff grabs and holds. I learned the hard way too, had a whole mosaic do the same slow slide. What a mess to clean up.

Consider returning it first.

But is that actually a problem? Some people just work that way, keeping a bunch of tabs open as their system. Maybe his computer was old too.

That's a clever fix. My first try at something like that, I ended up making a small dark spot look like a cartoonish black eye on the wood. It took more work to fix my fix than the original stain. Your method sounds much more controlled.