Tennis requires two people. It’s boring with just one person hitting to the other side of the net with no one there.
Teaching a language is like that, because human communication is reciprocal and participatory and back and forth and very Vygotsky.
So we kind of need to get something back from our students when we teach using comprehensible input. But what if they don’t speak the language?
No matter. We just ask a bunch of questions. A class can light up* with them saying nothing but yes an no. Unless we want to play solo tennis.
*They light up when you loosen up.