People with introverted traits can seem like they have no problem socializing; they may be able to trade quips, be quick witted, put on presentations for school and work with seeming ease. Introversion is not shyness, social anxiety nor avoidant behavior. Just because introverts can pull out the social fireworks when necessary does not mean that they are not in fact introverted or are faking it. You don't know how "passing" by being social and extroverted in a given situation affected that person. Ultimately, introverts do have different needs for self care than people who tend to be more socially oriented. Rather than jump to judgement, try to sit back and learn. Talk to the introvert, instead of assuming you've got him all figured out. The best way to find out more about your friend and how you can help him feel more comfortable is simply to ask him.  Friendships are wonderful things to nurture, and the point of friendship is to get to know someone, care about him, and keep his best interests in mind.  Take the time to find out about what introversion is like for your friend, what his challenges are, and how he feels. Ask concrete, complete questions, as these types of questions may be easier for someone with introverted qualities to answer. Your friend may feel relieved that you are taking interest and showing that you care.  Here are some questions and suggestions you may want to start with:  What are the easiest social situations for you to be in?  What kinds of social situations are the most tiring? Is there anything I can do to help you when you feel socially overwhelmed or drained? Do I ever make you feel uncomfortable or overwhelmed in social situations?  How can I help ease that? This rule is important and is often the hardest for most extroverts to understand. Introverts like people, but their inner electrical systems are wired very differently. When they're grouchy, crotchety, or just tired, they need time to themselves.  If extroverts are solar cells, absorbing light and energy externally, then...

TL;DR in Vietnamese:
Tránh phán xét. Hỏi người hướng nội xem họ cần gì. Cho người hướng nội thời gian ở một mình. Hiểu và tôn trọng ranh giới. Chấp nhận giao tiếp. Lắng nghe. Mời và đáp lại sự trung thực. Thích nghi. Trở thành bạn.