I was scolded heavily as a young child for talking out of place, so that left me being very quiet and not knowing when to speak up, and being afraid to do so. So everyone just assumed I was shy or timid, and later just unfriendly and not social.
It wasn't until way later in life that I realized just how bad the social anxiety was. I'm doing better thanks to understanding friends, but it's still a daily struggle, so I know exactly the feeling.