I just realized I never answered the OP's original question.
In my case, I always had an interest in Japanese culture, studied Japanese literature in college and grad school, and then decided I might want to try living here.
As it turned out, I enjoyed living here more than I did living in my home country (the United States), so I decided to stay. Now my job, my friends, my wife, and pretty much my entire life is centered in Japan, and I'm quite a bit happier than I was in the US, so I'm glad I made the decision to stay.
Not that I would necessarily encourage anyone/everyone with an interest in the culture to move to Japan. To each their own, really.
Nobody can tell you where you'll find happiness—it's something you have to discover for yourself.