John Bender / RIPR

Investigators say a clamp that held up an apparatus snapped, sending eight acrobats plunging 35 feet to the ground, falling on a dancer below. It happened on Sunday during a circus act where women dangle high above the ground from their hair.

Most people have heard of the "Three Mile Island" nuclear power plant accident of 1979.  But it's famous among engineers for being a "normal accident", in that there wasn't any one thing that nearly caused a meltdown of catastrophic was a series of little things inside a highly complex system that all happened as part of "normal" operations.   None of which, by themselves, was terribly problematic.  But they all happened at once, and that was a problem.