One of the most common issues I see with teens and young adults is isolation. Sometimes isolation is simply the answer to how a person protects themselves from social rejection. For others, isolation is introversion without boundaries. People isolate to protect themselves from the rejection, pain, or trauma of others or to feel comfortable. No matter what the reason, the common thought is that isolation is never viewed as "isolation" by the person who is alone.
Don't get me wrong; isolation is NOT needing to take a break from people, needing alone time, or having a desire for peace and relaxation. On the contrary, a balance of interaction and alone time is good for people. Isolation IS when there is a persistent pattern of withdrawal from human interaction and the building of relationships.
For those who are consistently avoiding relationships and social interaction, they see their own isolation as just "who they are". And for introverts, this line can be blurry and take time to figure out. Most teenage guys who are isolating themselves are either A) playing video games or B) watching TV. Both of which aren't inherently "bad". The problem is that an activity like a video game is a distraction and also a great way to numb out any pain. The same goes for television, youtube, or most other media. In other words, they help the person detach from their own world. I won't tell you how much is too much or make a judgement call on that. I think the line is different for different people and different times of life.
I'm not saying that the solution is to rid the world of video games or television. But for kids who struggle socially, the first step is for YOU (Mom or Dad) to help regulate media in a way that approaches a balance in their lives.
"But maybe my kid is just an introvert. Shouldn't I accept him for who he is?" Yes, accept him for who he is. But if you're reading this then it likely means your kid is also unhappy in some capacity or struggling with self-esteem and isolation.
There's a very important concept in the world of dialectical therapy which is that you can accept yourself and love yourself for who you are AND also push yourself to change. It's not either/or. It's BOTH/AND. I accept myself, flaws and all AND will continue to push myself to change and be a better Husband, Father, Leader, Therapist, etc.
So, accept your child, flaws and all for who they are AND help them find ways to grow and change.