I've had this theory since my earlier days in this industry known as indie-filmmaking. Much like summer camp when you're younger and college groups when you're older, being around the same group of people after 12-15 hours a day for 3 weeks plus can only result in emotional and/or physical attraction if you're single. This, my friend, is known as 'The Ten-Day Syndrome'. Someone who you thought was a nice girl/guy during day one of shooting suddenly turns into someone who can bring a smile to your face just by walking near you by the time you've reach day 10.
Perhaps this blog entry is more exclusive to my film colleagues, but I'm sure most people can relate.
(Note: Thanks to Alexandra for the pic above)