If you look up the word "introvert" in the dictionary, you'd most likely see a picture of Sheldon Cooper right next to it. Sheldon doesn't do socializing, unless it's with Leonard, Howard and Raj sat in front of an Xbox or watching Star Trek. It probably won't come as a surprise to learn then that Sheldon doesn't have much luck with the opposite sex - or at least, that's the case until he meets Amy Farrah Fowler. Amy is the female equivalent of Sheldon and is enamoured by him, but goes on a date with Stuart from the comic book store when Sheldon rebuffs her advances. This makes Sheldon jealous, and he crashes the date at the cinema and introduces the "relationship agreement". How, erm, romantic.