If you spoke English and moved to Spain for three months, and you spent an hour or more a day actively attempting to learn the language, you would catch on very quickly.
German, for instance, turns out to be a lot harder than Spanish, which I'd learned when I was younger. I've been in Germany for 7.5 years, have had girlfriends I only spoke German to, speak German with most of my friends ... and I still struggle with getting the grammar right.
Once again I find Tim's take on things horribly over-simplifying. It seems that he makes rather audacious points by redefining words (e.g. "work", "fluency") and then drawing a bunch of conclusions based on those redefinitions.
I'd guess it's the "learned when I was younger" part that made the difference.
I would like to tell you that you are most certainly wrong. Although I can have a simple conversation in a social context I have a lot of trouble understanding the fluid discussions of native speakers. I have met many people who have moved here and are attempting to learn the language and can attest to the fact no one learns in 3 months. 12 months is closer to reality and even then the level will be extremely basic.
I also picked up a Japanese novel yesterday and am having quite a bit of difficulty reading a scene in which the protagonist is sparring with someone wielding an axe because my vocabulary with respect to hard bits on swords and soft bits on people is rather more limited than the book expects of me.
(If you think the bit about learning Japanese can be compartmentalized away from the bit about learning to persuade or learning what big megacorps value in new products, I respectfully disagree, but you'd probably find the answer "3 years college, 1 year study abroad, 3 years professional experience in (mostly) J->E IT translation, 2 years in software development/management for aforementioned megacorp" more useful.)
I was exactly wondering whether you just learned that language a few years ago and you'd somehow mastered it to this level in a short time or if there were some circumstances that would explain your proficiency better. It's quite rare to find anybody that spends even a moderate time in Japan to know the language at that level.
A good friend has her degree in Japanese and she would not even begin to claim that she's either fluent or comfortable in the language, and that's after 5 years of studying it intensely. To her it's a 'good basis to start learning Japanese', which she says is almost impossible outside of living in Japan for an extended period. It's against that background that I'm impressed, I know a little bit of how much effort that must have been, even if plenty of it went 'as you go' by immersion.
I think that I was looking for exactly the first two words of your reply.
My own 'second mother tongue' (English) I've been learning since I was 10 years old or so and I'm still learning, there isn't a day that I find some turn of phrase that I hadn't encountered before. I've also noticed that speaking a few languages helps to make you (much) more forgiving towards others in a foreign tongue.
Do you come across many foreigners in Japan that have your level ?
Tim Ferris is claiming that he:
1) Learned to understand
2) the oral instructions regarding
3) a single simple, limited domain
4) from a single speaker or small set of speakers
5) in a very rote, ritualized context
Back in the real world, you will frequently be called to:
1) Read, write, speak, and listen to
2) an unbounded variety of discourses (including "instructions") regarding
3) an unbounded variety of topics, many of which you have little prior interest in (such as "Compelling Reasons To Not Arrest Me")
4) from a very diverse set of speakers numbering in the millions, representing many dialects, speaking styles, social statuses, verbal ticks, and dispositions with regards to you (such as "Skeptical Small-town Policeman")
5) in a variety of contexts ranging from heavily rote conversions or ritualized interactions to extraordinarily fluid situations which you you may never encounter prior to really desperately needing to perform well in them.
(Cards on the table: I think "fluency" is a poor goal because it is confoundingly difficult to measure. I tend to advice folks to phrase goals for language learning in terms of tasks they cannot currently accomplish which they wish to be able to accomplish in the future. "Am I fluent?" is hard to answer, "Did I understand the Deployment Instructions well enough to actually boot the server?" is easy.)