[andai]

I learned this from Zed Shaw's Learn X The Hard Way books. He says this approach is mainstream in other disciplines, like music, languages, or martial arts.

I also heard the philosopher Ken Wilber spent a few years (in what kids today call Monk Mode) writing out great books by hand.

The main effect I noticed is that I rapidly gain muscle memory in a new programming language, library or codebase.

The other effect is that I'm forced to round-trip every token through my brain, which is very helpful as my eyes tend to glaze over — often I'll be looking right at an obvious bug without seeing it.

[djtango]

Just to add to your point, both Mozart and Chopin were known to hand copy JS Bach's well tempered clavier preludes and fugues