Yeah! That is one major school of thought, popularized by Stephen Krashen. Called the input hypothesis, you might see the term “comprehensible input” used to refer to the same idea or set of ideas. The intuition behind it is that plenty of adults move to a country and get nothing but natural language input day in and day out for months or years, and they don’t acquire much (or sometimes any!) language this way.
There must be something that explains why this happens, and he points to the idea that you need to be understanding at least a part of the input to get some benefit from it. This seems more than plausible, especially for adult language learners who are using their cognitive faculties to learn a language as opposed to the kind of acquisition that happens during the critical period with your first language.
Other possible explanations focus less on do with what you actually can comprehend vs whether you are trying to comprehend vs not trying to comprehend. Think of how you might kinda turn off your brain when listening to a song in your first language and not actually pay attention to the lyrics, vs actively looking at those same lyrics if you were learning it for karaoke. If you go around with your brain switched off not trying to understand anything, it makes sense that you wouldn’t pick up much even if you were constantly surrounded by input.
There’s other explanations too, language acquisition is important in a lot of different areas of study. Some from psychology treat it more like any normal skill acquisition (where again, consistent practice is important), some from sociology and sociolinguistics treat it more as a cultural thing (where you mainly learn language through active participation in a community)
Likely, it’s some combination of all these things: adult language acquisition is part skill practice, part active comprehension with lots of exposure, and part community participation. Importantly, none of these things really exclude the other and can actually overlap quite a bit! It’s kind of like looking at the same picture from 3 different sides.
But in all of these possible explanations, one thing that stays pretty consistent is that language (especially second language) is really a use it or lose it kinda thing. If you take extended breaks, your language skills will rapidly deteriorate. If you stop practicing, stop reading/listening to stuff, or get cut off from your language community, you will start to lose your proficiency. (It can come back, of course, but only if you start working consistently again!)