You start the coffee brewing, go eat your Pop Tarts and play on the internet, then come back to find the coffee's done.
Only, you forgot to actually put in the coffee. So what you've made is a pot of hot water.
Luckily, I was up early enough I could start the process over and still get to work on time. If I hadn't randomly snorted myself awake when I did (I slept AN HOUR PAST the alarm) that wouldn't be the case. But, as luck would have it, my own obnoxiousness awoke me on time.
True story, as my daughter would say.