In August 2011, Los Alamos techs posed 8 plutonium rods on a work table to take a few photos.

Had these rods rolled into each other there would have been an instant criticality event. (Think "Demon Core")

Worst still, a supervisor who saw the display ordered the techs to safe the rods, ignoring the protocol to evacuate EVERYBODY (b/c even a hand could moderate the neutrons & cause criticality).

It caused a 4-year, billion-dollar shutdown.

...

Smart people + overfamiliarity = stupid things.