Oh I feel that, very much so...I think it's really difficult to accept that as a beginning writer; realizing that the average 'normal' protagonist-- someone adventurous and outgoing who can easily make social connections-- is simply not something you can write authentically.
But A, you don't have to write 'normal' protagonists, and B, as much as it's true that nothing comes from nothing, it's important to also realize that you are NOT nothing. All the life experience in the world won't help you if you can't also learn to broaden your perspective and realize that there's more than one way in which a life can be worth living; more than one type of person whose story deserves to be told.
Of course, when I say 'you', I mean anyone else who's reading this and feels like the OP resonated with them. ^^ But my point is that it's unlikely that you will ever stop being an introvert, so you have to appreciate that worldview for what it is. Pay attention to yourself, look inward and take note of all the emotions you experience: your frustrations, your fears, your struggles, your triumphs. They may not be loud enough for other people to hear, but they still exist and they are human.
Any story or character that you write, even if it relies on fantastical experiences to take the place of the ones you never had, will be stronger for that understanding.
And when you go out and do the things you do, and speak to the people you meet, it'll help you to relate their experiences to your own. You CAN use other people's life experiences to supplement the stories you tell, but it'll be easier to understand them and internalize them if you think of them not as the experiences of someone who's alien or 'superior' to yourself, but as those of just another human being, who probably goes through a lot of the same things that you do.
