Don't get me wrong - many introverts can talk to strangers just fine if they need it (just as I can lift 50 lbs if I need it), it's just something they don't particularly enjoy doing. It's work. If it needs to be done, it will be done, but if it can be avoided - it will be avoided. I am not sure one needs some training to change that - if I don't enjoy doing something, why waste time on doing it if I could instead do something I already enjoy doing?