Only 20% of people try to stop a murder on an elevator.
http://www.cnn.com/video/?hpt=hp_c3#/video/world/2013/03/05/tsr-moos-would-you-stop-a-murder.cnn (http://www.cnn.com/video/?hpt=hp_c3#/video/world/2013/03/05/tsr-moos-would-you-stop-a-murder.cnn)
I didn't watch the video (annoying 30 second commercial - how's that for ADD), but my best guess is self preservation; most people aren't educated in the martial arts, or are packing...
They're calling the cops, man!