I agree with this. That's why I carefully chose the phrase "to function in". Grasping and understanding Japanese culture is quite doable. It's internalizing the myriad social rules and operating under them smoothly which is the challenge. And it's a challenge I don't think is worth the effort, because Japanese social rules are a very tight straightjacket. My life as a gaijin in Japan is much more relaxed and easy, and I can do many things that Japanese don't just because it isn't the proper social thing to do. I knowingly and willingly cross all sorts of lines in Japanese society that natives won't. I do this understanding what I am doing. Grasping Japanese culture and social mores is one thing. Being able to operation smoothly within them is another thing entirely.
Ah, I seem to have slightly misunderstood you, when you said "function in", sorry about that!
If I understand you correctly now, you meant the difference between "understanding" and "becoming", correct? For instance, with proper study, I can understand the mind of a psychopath, but that doesn't mean I can just become a psychopath myself (I may well be able to act like one, if needed, but it isn't "me", so to speak).
Is that correct?