Tragedy is perceived as a reversal of fortune, a fall from a high position.
This view of tragedy derives from the Medieval concept of fortune, which is personified as Dame Fortune, a blindfolded woman who turned a wheel at whim; men were stationed at various places on the wheel--the top of the wheel represented the best fortune, being under the wheel the worst fortune.
However, the wheel could turn suddenly and the man on top could suddenly be under the wheel, without warning.
