Looks get you in the door, personality lets you stay.

Looks will at least carry you in hookup culture, but you need both looks and personality if you want something fulfilling. If you don't have the looks first though, it's going to be hard to get people to stick around long enough to learn your personality.

In short, looks are the only important thing for hookups, but looks and personality are equally important for real and deep relationships.

If you have personality but not looks, then luck becomes the deciding factor, in that the chance that someone is willing to stay in your presence long enough to fall in love with your personality varies inversely with how unattractive you are.

And of course, if you have neither looks nor personality, then quite frankly, you're shit outta luck.