Below, this post will argue that there are only three roads to mastering Chinese. This being the case, we need to have a very strong motivation to keep spending time with Chinese.
Road to mastering Chinese #1: Using Chinese in your job
If Chinese is an integral part of your job and you encounter different native speakers on a daily basis, you are sure to learn a ton of Chinese. Naturally, you will learn more if you actually focus on studying a bit on the side, too, but the exposure and amount of practice you will get will accumulate over the years even if you don't study. Most people spend perhaps one third of their time either working or on work-related things, so if this involves Chinese, you will get to 10,000 hours and beyond in no time.
Road to mastering Chinese #2: Cultivating a genuine interest
Some people spend more time on their hobbies than they do on their jobs. If you can make Chinese the target of such a strong interest, you're likely to be able to reach mastery sooner or later. This will power all kinds of useful process, such as turning most of your life into Chinese. Instead of listening to Western music, you listen to Chinese music. Instead of reading books in English, you read everything in Chinese. You might also move to China, but this isn't necessary. With a moderately strong interest, you can get pretty far, but you need a genuinely strong motivation to reach mastery.
Road to mastering Chinese #3: Having your social life in Chinese
In the draft of this article, this third and last road to mastery was called "marry a Chinese-speaking man or woman", but that seems to be a bit too narrow. The point here is that a majority of your social interactions need to be in Chinese and for many people, this means marrying a Chinese-speaking person, but it is of course conceivable that you could achieve the same by only having Chinese-speaking friends. Naturally, simply having someone who speaks Chinese around doesn't mean anything, of course you need to speak Chinese as well. This gives you the opportunity of really learning the spoken language, but probably does little for your reading and writing.
You don't have to live in China
Of course, many things will be a lot easier if you live in China, such as marrying a Chinese person, working with Chinese or maintaining a strong interest in the language. Many of these things might happen automatically, but if you're not living in China, you will have to make an effort. Still, it's a matter of different degrees of difficulty, not a matter of possible or impossible.
Different roads, different destinations
It should be obvious from the above discussion that mastery is a pretty broad term and that it incorporate a lot of different skills. The roads I have talked about in this article aren't equal when it comes to these skills. For instance, a strong interest is probably the only thing that will make fully literate in Chinese and what kind of job you have in Chinese matters greatly. For instance, compare my situation with someone who works with interpretation.
It's not the case that you have to choose one of them or that you can't reach your goal if you miss some component, the goal here is to show that since we need to spend so much time, we'd better find ways of doing it that really matter to us and that make Chinese an integral part of our lives, not just something we study.
Please visit Chinlingo for Chinese learning.