The author wrote a story about his students when he was teaching them mandarin. It was at a two-week accelerated mandarin learning class. One of his students went by the name of “Michael”. Michael was trained as an engineer and was working as CEO of a medium-size operation. For work or  some other reasons, he thought it was time to take mandarin seriously. He had lived in HongKong for many years but he did not know Cantonese. Why did he not think he needed to learn Cantonese but mandarin? I guess that at that time, china’s mainland was starting to open to the outside world. Many people came from the Chinese mainland to HongKong to work or live. Those people from China’s mainland did not speak English. Most of the locals in HongKong speak English. Because at that time HongKong was still governed by the United Kingdom not returned to the motherland yet. If the locals could not speak English they might not get a good job. Therefore Michael needed not bother himself to learn Cantonese. As more and more people from mainland China to HomeKong, Michael needed to communicate with people from China’s mainland in his work or life. So he had to bother himself to learn Mandarin Chinese. He enrolled in the author’s accelerated mandarin learning course. Two weeks, just two weeks. So you can imagine the pace the class would be. Michael cracked along the course pretty well. He got the sense of how Mandarin works as a language. He built his vocabulary really quickly. But there was a strange problem. He could not pronounce some mandarin words correctly. He pronounced them with a strong accent just like a Cantonese native speaker speaks mandarine for the first time. Although he did not know Cantonese but he was surrounded by Cantonese for several years. He had absorbed Cantonese unconsciously which affected his mandarin accent. A ghost of unknown language.
     So you can not stop learning languages no matter the first language or the second language. It is obvious that you can not stop learning your first language if you are not deaf. You came to the world with no words or grammar to hook on to, you somehow mastered your mother tongue. In many countries like India, Dutch, people all are able to speak a number of languages without extra effort. Since in those countries, these several languages are used as interact mediums simultaneously. So they picked up the languages naturally.  We can draw the conclusion that humans are born with the hard-wire to learn languages. Your brain naturally is a language processor. You can pick up languages naturally. The question is when we learn a second language and there is no this language environment, how can we treat it as our first language and learn it naturally? I hope I will get the answer.