This reminds me of something... I'm a jazz musician when not being a coder, and have studied and taught from/to a lot of players. One thing advanced improvisors notice is that the student is very frequently not a good judge – in the moment – of what is making them better. Doing long term analytics tests (as the author did) works, but knowing how well something is working while you're doing it? not so much. Very, very frequently that which feels productive isn't, and that which feels painful and slow is.

Just spit balling here, but it sure feels similar.