The old saw, "Comedy = Tragedy + time" is absoluetely true. I think of the old Monty Python routines regarding the Spanish Inquisition or the Black Plague - how horribly insensitive! Why are we laughing? Because everyone who suffered these unspeakable horrors, and all the people who knew someone who suffered them, has been dead for centuries. So we can guffaw when we watch the "Bring Out Your Dead" scene in the Holy Grail movie.
It is a lot tougher to laugh about something horrible that happened recently - like the 9/11 attacks or the Japanese tsunami. But I can imagine my great, great, great grandchildren having a jolly time making fun of the silly little messes that all of us ancients managed to get into during the olden days.
It is easier to laugh about your own pain, of course. I can laugh about my teenage angst now, but it was deadly serious and horribly tragic when I was living through it. I can laugh about all of my failures in business, but the stress of those experiences nearly killed me. I can laugh about the bones I broke when various accidents befell me (doing a header off my mountain bike, getting slammed in the ribs by a rapidly opening car door, etc.), but I don't remember finding those injuries to be funny when they happened. So the elapsed time between tragedy and comedy can be shorter if you are the sole protagonist.
I think that this weird method of coping, laughing when contemplating past nasty stuff, is part of our evolutionary adaption. Without the ability to laugh at these things, life might get so dark that living is no longer worth the effort. We laugh to survive.
