With hundreds of millions of ugly guys who all are attracted to 10's, I bet the 10's would be hiding in their houses or trying to pass some kind of public sexual harrassment laws or something if all the guys took this advice.
I said "if you have a chance with her". Not a chance to approach, a chance to succeed. Some girls would find you more attractive for reasons beyond looks.
And as for her looking better than you, what I meant is if you look better to her than the typical guys she is used to dating. If you were just as attractive as the typical guy she dates, and then she finds out about the piece, that then may put you below average, and increase the chances of her breaking up with you or finding someone better.
But again, you are disregarding the notion of attraction, which is built from more than just looks. Two guys might look very similar, yet the same woman is very attracted to one and not at all to the other.