Dark Dragon

Hi, I never understand how a person can know someone for years and be like the perfect person for you but they feel in love with a person than they just meet and don't know nothing about it. I saw it in many movies and people around me, how like have someone that say that is perfect for them but not because the are friends, and later the are sad because the person that the just meet isn't what the expect. And other is people how need to have a crush or be in love to be happy. Or this people who like to date bad boys or girls because they think that they can fix them, like why they date them in the first place if they want to change them?