Inferiority is one of the reasons. We should believe that no one is worse than others, only those who don't work hard. Some people were reluctant to speak when they were young, and now it has become an obstacle to speak. So you just need to know when you need to talk and when you don't need to talk. You don't need to speak when you don't need to speak, but you must summon up courage to vibrate the Adam's apple and make your own sound, because you may lose an opportunity or some benefits just because you don't speak. Of course, you can go over the lines in your head first and organize the language.