That moment when the mac mini that holds all your stuff doesn't start. You push various combinations of buttons, nothing. You begin to think of how old the computer is, how it's been on 24/7 for four or five years, all the stuff you keep in it (but that is kind of secondary in that it is all backed up). Reset SMC. Nothing. Leave it till after I've had a shower and a first coffee. Then, unplug everything from the USB ports, press the button... and it starts. Phew.