If you have enough guts (especially self confidence and esteem), most of the time (not always), you can attract and be successful in front of your out-of-the-league person.
Every day, we see a lot of average looking guys with drop dead hot ladies. Why? Because they were confident about themselves. Of course they didn't have (the major) appearance advantage but they knew what to talk and how to talk. Their intentions were clear and didn't expect that much as daydreamers do.
In my experience, I think the biggest thing is men and women want any sort of attraction/beginning relationship to be super intense feelings wise, so they select people who have an intense chemistry with them regardless of whether the person is a good match for them. Then they try to change each other into the person they want the other to be. This leads to resentment and the relationship falls apart.
In the event that the person in question does keep their head in things and recognizes that a person isn't a great match then the person is villified as being stuck up, arrogant, or any number of other things. Because everyone thinks they are a great person, but sometimes 2 people can be great and not be right for each other (which is very hard for some to grasp).
Lastly if 2 people are very compatible and a good match, if the chemistry isn't instantly electric some people will say there is no attraction. Most people don't realize that love grows with time and that instant chemistry isn't real love. Attraction must be there, but sometimes I think if a person makes sense then people should give it more of a chance.