I mostly prefer to go out with people, but I have some interests/tastes that the majority of my close friends don't share (mostly theatre and films) so I'm happy to go do that stuff alone if I have to. Obviously we have some stuff in common or we wouldn't be friends, but I'll still go see movies and do stuff I'm not
that interested in with them because
a) you never know it might turn out to be good/fun
b) even if it's shit I'm there to hang out with my friends and have fun with
them, not be blown away by the cinematic genius that is the Twilight movie or be thrilled by hours of shoe shopping.
Also I go shopping and to libraries and stuff by myself all the time, I don't get people who won't do this. My little sister will not even catch the bus alone, anywhere. She's 17 btw so I find it weird. She's well old enough to transport herself around the joint and do her shit but she'll either wait til I can drive her and come with, or arrange an expedition with all her friends