Proper pronunciation is the key to learning English. The vocabulary you know will not be effective for communication if it is not pronounced correctly. It is much better to know a few words and speak well than to know many words and speak badly. When you speak using the right sounds, it can help people quickly understand what you are trying to say so that communication will occur and succeed. On the contrary, when you speak with poor pronunciation, it can lead to misunderstanding that may further lead to disaster. It can also make people avoid talking to you because they think you are too hard to talk to.