Even fictional characters know the importance of the first principle — If you can’t do without it, make sure you won’t have to.  Acting on this knowledge is what marks them as professionals in the eyes of the other character in this passage from my favorite early work by one of my favorite writers:

“Now,” Lucas said, “when Two-a-Day’s hired help, who are all in all a pair of tough and experienced console jockeys, when they saw what you are about to see, my man, they decided that their deck was due for that big overhaul in the sky. Being pros, they had a backup deck. When they brought it on line, they saw the same thing. It was at that point that they decided to phone their employer, Mr. Two-a-Day, who, as we can see from this mess, was about to throw himself a party.”

~William Gibson, Count Zero

I know. I’ve just betrayed a little geekiness in my ready habits. Just substitute “AV tech” for “console jockey” and “projector” for deck”. Okay, that’s still pretty geeky, but you get the idea.