The Impact of Comprehensible Input on Language Learning

In the 70s, Stephen Krashen published his work as hypothesis on language learning. It was actually made a real big impact in the language learning community. He said that you don't really need to learn grammar. You don't have to actively study it. Whereas conscious learning is not really effective. So how do you actually teach then? Teachers that had 20 years in the classroom are being told what they've been doing their whole lives doesn't work.