Oh yeah, totally, immersion in the native environment is the only way you'll completely grasp a foreign language in the end, especially something like Japanese. I'd say I was already pretty competent at Japanese before I last lived there; I communicated with native friends in it pretty regularly and as I've mentioned elsewhere, I did a lot of optional studying on the side constantly to make sure I knew more than I was obligated to know for classes. But I wouldn't at all compare how I was back then to how I am now, positively. I'm still not perfect at it, but going over to Japan helped with my fluency immensely in two ways: 1. It gave me a much better sense of how different grammar points and colloquialisms are applied naturally and 2. It gave me the confidence to build up my knowledge of the language using material already written in that language. Prior to going over there, I'd spent my third year of Japanese studying from an entirely Japanese language textbook and taking classes that were conducted mostly in Japanese, but that was only for 50 minutes a day four days a week. Over there, though, it was do or die and not only was I continuing to study Japanese exclusively in Japanese, I had to engage my professors exclusively in that language even outside of class and I had to do so for a minimum of two hours a day five days a week depending on my daily schedule before factoring in homework and independent study, which was also all in Japanese and was usually three hours a night minimum. Mix that in with just going about daily life with verbal and written Japanese completely surrounding me outside my mostly English-speaking dorm and I'd say that the different was day and night compared to when I was studying it in the States. One of the many reasons I'm working on moving back to Japan aside from just liking the place so much is in fact because I can't really use it in my daily life in the States outside of work and I worry about my fluency slipping if I let things simmer much longer.