The times when I have felt I am missing out have been the times when I have not been happy with myself or what I’m doing.
Here are some things that look really fun but that I would not be missing out on because I don’t find them fun:
A large group of people traveling together (as an introvert traveling with others is very stressful and exhausting)
A bar: Rowdy, noisy, crowded. I’d much rather be home in the company of a good book.
A party: I crouch in a corner and wonder how soon I can leave.
There are things I do that are really, really fun. I don’t want to miss out on them but if someone really extroverted saw my photos they would probably be OK not being a part of them:
Drinking coffee and reading the news
Cooking. (OK. Watching my boyfriend cook while I loiter around the kitchen tasting things that aren’t ready.)
When I am true to myself and what interests me, the feeling that someone else is having more fun than me goes away completely.