I think that we all love to love the underdog. The one who seems so sweet. the one we don't want to see get hurt. In reality we need passion in relationships and looks do matter. If you aren't attracted to someone (no matter how sweet and nice they are) the relationship will fail. Adam had a passionate spark for Sam that he didn't have with Rachel. We shouldn't get mad at him for falling for the one he was the most attracted to and had the best time with. We should be happy that two people found each other and want to bring joy into each others lives whether it be short or long term.