[hrktb]

I think the point is really to have a strong interest in the language. Not just an accademical curiousity, but something that is stromg enough to force the brain to go painful places, cram unordinary amount of new concepts and throw ourselves completely outside our comfort zones.

For most people it's a signifiant other, or just living in a foreign country where not understanding is more painful than doing the effort to learn. As an anecdote, a few people around me got to learn japanese by sheer passion for the culture, as they were breathing it day in day out anyway. We could say their games, anime, manga, novels and tv drama were kind of their S/O, if only by the amount of time it took in their daily lives.