(I know, restarting the server != rebooting the machine.)
I had to go to one of the more "exotic" server rooms, placed in a basement and saw a very old desktop stuffed on the bottom of a rack. Covered with dust, open side panels, plastic turned yellow, you know how old and forgotten hardware looks like. This had a new-ish post-it with the message: "this runs all of the fax infrastructure. you turn it off, you explain it to the CEO".
They started bouncing paychecks before I got to see the drama come to a head, but I'm obsessive about proper levels of redundancy anymore. Don't build fragility into a system, and at least leave yourself a means to fail gracefully.