There are many things further down the road to go wrong with attractive popular girls. 2 most catastrophic cases in my life are with those such as them.

Admittedly I'm the one who mainly failed them due to misunderstandings and passiveness, but when a girl (being all that popular) is used to boys being rather active and competitive and social, and then you are here just cause she happened to like your looks, this may end painfully, for you more than for her.

There are also cases from the post, only I may have noticed, just wouldn't risk losing an existing good friendship for possible romance.