I have failed for all of the usual reasons:
inconsiderate 'tourists' stepping right in front of my camera on tripod
a passerby wants to engage in a conversation about (fill in the blank) as the light passes
no film in camera
failure to remove the lens cap
failure to close the preview lever after GG focusing
Failure to pull the darkslide / failure to replace the darkslide
dropped camera in parking lot / destroyed lens on arrival at event.
a drunk wedding guest mistakenly picked up my camera and walked off with it
chased off by private security.
wind/weather/clouds no cooperating.
but, I cannot really think of anything strange...