According to Krashen, effort is not needed for comprehensible input to be effective. Rather, it is more likely that you are simply not consuming enough comprehensible input
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.
Krashen is brought up a lot as a "magic bullet". But I think there are 3 big caveats to his work that often don't get brought up.
- The amount of comprehensible input needed is really huge. So much so that someone who has 10-20 hours a week to learn a language might be better using an active approach.
- I used to think that if you understood a language certainly you would also be able to speak it. But this just isn't true. Passive vocabulary and active vocabulary (not to mention sentence construction) are separate and need to be practiced individually.
- In my own experience I have been very successfull with comprehensible input when paired with being in the country or studying the language during the day. This allows me to solidify links from what I've heard and read with the real world. AFAIK, his studies had a similar setup, always including students who were studying the language and then did extra reading/watching on top of that.
There is a bit of a pipe dream, that you will just watch mangas all day at your level and suddenly come out fluent.
I wonder if the nature of internet discourse has also changed, reducing how much there is. Comparing wiki.c2.com style pages/discussions with reddit now, things evolve in a much less coherent manner, there is less of a conversational back and forth truly developing ideas and more of a show-offy approach. Perhaps topics are also more difficult - e.g. learning CSS today with 30+ units of measurement must be hell compared to back in the day.
