Here are three separate but similar things: shyness, introversion and social anxiety. You can have one, two or all three of these things simultaneously. A lot of the time people think they’re all the same thing, but that’s just not true. Extroverts can be shy, introverts can be bold, and a condition like anxiety can strike whatever kind of social animal you are.
Lots of people are shy. Shy is normal. A bit of anxiety is normal. Throw the two together, add some kind of brain-signal error – a NO ENTRY sign on the neural highway from my brain to my mouth, perhaps, though no one really knows – and you have me. Silent Steffi.