This one's for all those who've ever been innocently going about their business and the suddenly had their lives irrevocably changed (I was going to say fucked up, but I realise that may not always be accurate). You can blame this punk:
[Unapologetically nicked from Red: I'd wager there's no armour that can stop those arrows!]
Or, for those inclined to a more scientific explanation, try this Time Magazine bit - recommended by a relationship psych scholar I know. Me? I sorta prefer the fat guy on the hill - seems to capture the effect a little better.
Happy Valentines Day, y'all!