I think we all want a person who is attractive with a good personality.
The problem however, is that we have a nice person who wants someone but the person they find attractive does not want them. This leaves the person sad, which is 100% understandable but it does royally suck.
Also, we don't know the reasons why the other person does not like them back because they are not attracted to them
Then we have the person who does not like this nice person back because they do not find him or her attractive. However, this guy or girl likes someone else and he or she does not like him/her back
And thats just the less complicated part of the cycle. Now lets evaluate the cyle and start back to the beginning.
Guy or girl likes person, then wonders why the person they choose to be with is bad and then suddenly realizes what he or she may be doing wrong. Leaves said person. Yet still has no clue that the other person that likes them, or once they realize they like them they may be too prideful to say something if they like them back.
Then, we have the person he/she likes and they realize they are meeting the wrong people that don't treat them right, they leave said person and they go back to the beginning of the cycle.
What sucks about this cycle is just because a person has a good personality, is nice, and attractive, they may not be attractive in the eyes of the person that they want.
Then the person ends up falling in love with someone who may not deserve their love because they are rude or mean. In a perfect world, nice and caring people would end up with other nice and caring people who they find attractive, but what most people fail to see in this cyle is.... the feeling has to be mutual
(Disclaimer:These are my opinions and are not to be seen as a rule of thumb)