1) Girls will, in general, like guys more if they're more outgoing
While you will always have the girl who prefers a reserved, modest guy theirs a massive influx of girls who prefer guys who are very outgoing...the more the better. For instance, if you hang out with your friends and you do the most talking it's highly likely the girls will take a lot of notice of you. This is more across the board than any other trait for men, even looks and money except in instances where the guy is far higher up than the people around him but in most cases people hang out with people of similar means so this doesn't apply.
2) Porn gives the opposite gender unrealistic expectations for your body
The only thing worst than the pressure people put on themselves to have incredibly "big" sexual assets is the fact that the opposite gender has been trained to expect them. Girls DO complain about guys being small and often say "well at least he had a big penis" even though it's widely accepted that an average one feels best. Similarly, many guys want a girl to have unrealistically big tits and ass and/or to be unnaturally skinny. "The Real Thing" is a not so exciting to them.
3) Some people are just naturals
Even if you have a great personalitiy, looks, money, career, talent...there's people who have nothing going for them and are insatiable to the opposite gender. They are complete trainwrecks as people and yet they are completely desired. Dating is not a merit based system.
4) The hottest people are often the most superfical
The reason that most girls value personality over looks is because most girls don't reach the gold standard for looks. Girls have a million million more expectations than guys could fathom, yet the ones who are seen as hot by all standards with which the words are used are often into similarly beautiful men. Highly superficial girls will have sex with a guy purely because he is good looking. This is because they buy into a plastic worldview where looks do matter...a lot. Yes, you see the occasional top ten girl with an average to guy but it's about as common as interracial relationships. I know this will piss people off to generalize but we're talking about the majority vs the minority here and if that makes you sad then I don't really care.
5) Men will never understand women, and women will never understand men
No matter what you do you will never understand fully and always have more questions. Eventually, you learn this doesn't matter but it does mean you'll never fully get along perfectly.