I'm not sure when I knew, maybe the first time I understood my Mom's explanation as to why I was mutely hiding behind her legs to a friend, "She's shy.".
Oh how I longed (and still do) to NOT be shy. I can remember watching Carole LaRoy captivate a big group of classmates in kindergarten, with her demonstration of "silent talking".
"Big deal!", I thought to myself. I do that all the time. Yup, I learned resentment of extroverts early on. All by myself. No one had to teach me. :>P
I know I missed many opportunities (of the social variety) over the next 4 decades and I hated it. I read books and articles and would even successfully push myself from time to time, but it was oh so painful.
It took a humiliating event in a store, where I couldn't find N, panicked and sought refuge in the car, to make me understand it was time to get help. I made an appointment with my doctor, explained myself and asked for help. Of course, he had to suggest counseling and I promised to seek it (which I did later). And then he wrote me a prescription. No, it's not a miracle, but what an improvement! How I wish I'd followed through and done something years ago!