I remember having anxiety attacks out on the playground when I was in kindergarten. I was so scared to talk to any of my peers. I'd wait until my bladder was practically bursting to ask the teacher if I could go to the bathroom, because I was so nervous and anxious about how to ask. Many times, teachers marked me absent and then later would realize I was there, and they'd say, "you were so quiet, I didn't even know you were here!"
I believe that I was born with a predisposition to social phobia and it was "triggered" by being forced to be around people in a school setting. I think life experiences, such as groing up in a dysfunctional family and having to endure verbal abuse by my own family and peers reinforced my anxiety and made it severe--it gave a rational "reason" to be afraid/anxious of people. I think if my parent's would have gotten me help early on, I might have recovered somewhat. But nobody recognized that there was a problem--everyone thought I was shy and would grow out of it. I'm 23. I'm still waiting to "grow out of it."
If I ever have a kid one day (which I highly doubt because there's no way I could have a relationship with a guy), I will not hesitate to bring my kid to a psychologist/psychiatrist at the very first sign of social anxiety or phobia--even if my kid manifests symptoms at 5 years of age. I would not sit back and watch my kid go through life with no friends, missing out on life experiences, etc. I'd rather be overly aggressive in getting help for my kid, even if that meant medicating a kid who's "a little shy" because I really believe strongly that there is a genetic component and I know first hand how quickly shy can turn into a severe, debilitating phobia.