[davisoneee]

Krashen is speaking with regards to languages. He doesn't expand on this to other fields.

It may well be the case that 'comprehensible input' is enough for languages because we already _understand_ at least one language to a functional degree, and there's no real 'learning' a foreign language, moreso _remembering_ words and structures. Much like most people don't 'understand' the mechanics of their native language, they merely use them.

I don't think that we can readily assume that comprehensible input is thus generalisable across other things we would wish to learn.