> Do you really think that if I isolated myself with hundreds of hours of say Mandarin audio recordings, TV shows and newspapers and novels and spent 40 hours a week listening to the recordings or staring at written text, that in a few months I would acquire the language?
Yes, it does work, according to various accounts I've seen, although 40 hours for a few months might not quite be enough
(the usual figure is around 18 months of full-time immersion, and more is obviously better), and this is actually quite challenging to do for long periods of time (esp. without distracting yourself with your native language excessively) and that's why it can be a challenge.
>not hundreds of hours of passive "experiencing".
It's on the hour of thousands, not hundreds. There are people, especially in the refold community, who have reached fluency in languages very different from their native, with mostly input (active output is part of the equation, but it can be done later, after your comprehension is very high).
>Speaking will not just "happen" if you don't actively practice it.
Yes, you do need to practice speaking to get good at speaking. But from aforementioned accounts, this process can be quite fast after a high level of comprehension has been gained.
I can confirm that for myself, over the past half year or so, increasing the amount of input I get every day has greatly accelerated my japanese learning process, versus the previous year, where I got far fewer hours in (1, maybe 2 hours a day at most, versus my current 4+ hours every day), although I'm not fluent yet.
In just that time I went from barely being able to read, and only being able to understand simple beginner podcasts to being able to fully understand easier shows (stuff for adults is still mostly out of my reach), and understand most of all the podcasts I listen to, (as long as I'm actually focused on the audio, if I'm passively listening I don't understand as much). My reading hasn't improved as much, as I spend probably 80% of the time listening/watching shows versus reading, but I can read basic manga easily now, and I'm working on reading through some essays now, novels still seems massively difficult, but we'll see in another couple months.
I've found that many hours of audio input each day have greatly improved my ability to keep up with native-speed speaking, although for increasing my comprehension, intensive study (making sure I understand each line in a show, or careful reading) is more effective per unit of time. I have no doubt you could acquire the same results as intensive study with enough exposure to the language though, as I've seen it happen with myself before I tried adding intensive study, it would just take more time.
Most people wouldn't call 4 hours a day massive though, so I can probably still increase my rate of improvement if I find more time to use.