Shy is bad. Why? Because if you come off as shy, people will think you're not a people person, not a team player, and lack confidence.
If they misinterpret your shyness, they may even think you're an arrogant prick who's too up his/her own ass and too good to talk to people.
As a shy person, I've seen number two happen way too many times -- I just didn't feel comfortable mouthing off, not because I thought I was better than you.
Now that I know people misinterpret my actions, I put on an act showcasing how extroverted I am to fit in -- yep, just an act, and now I do have a stick up my ass.