Why can't I be like a normal guy and talk to girls ?

Why do I never have the guts or motivation to talk to girls ? All my friends are brave enough to go up a some randon girls and talk to them but I won't even make a effort, infact I think I would walk out the club if they tried to get me a girls number. Also I get told I'm good looking and sometimes I like the way I look but I'm always very negative and never believe a girl would wanna talk to me. I'm a shy, quiet guy but even shy guys make a effort. I think its about time I had a girlfriend so any advice from guys with experience in talking to girls would be nice