Sparrow just had to be the first one to it! He accidentally falls in love because he wants to fit in with his friends and wants to think that desire is only based on the physical experience, and she's not hot (pretty though). That changes. Another example: you've never really noticed someone before, then you spend time with them (helping them or something) and discover that you see them all the time, always want to be with them. That's the beer-drinking chocolate-and-waffle-eating belgian's theory anyway.