First in response to the first question. shyness can take the form of reluctance, nervousness or outright fear. I think shyness can stem from modelled behaviour of parents, from frightening past events, or from limited knowledge or ability to socialize or interact on the same level as others have achieved. Not knowing how to behave in front of others - which of course is part of what you ask, which reveals the level of your shyness. Maybe the fact that its usually the opposite sex is a result of an inexperience in interactions with another gender.
I think only you can say how it can cause you to suffer loss as only you know what opportunites you miss out on.
My suggestion is to purposely put yourself in situations and dare yourself to talk, to interact, to be a part of things - as difficult as that may seem. Make it a habit. I'm shy myself - except when it comes to writing or work. Or one on one situations, groups - even groups of friends and family can render me - ME! - speechless and withdrawn.