I once did a service call on an ATM up at Vandenberg Air Force Base, about a 16hr day of mostly driving for me.
The new manager showed me the problem, the security light didn't work, and hadn't as long as he'd been there (about a month).
No problem! I'd brought enough parts to practically rebuild the whole ATM....but there was power to the lampholder
manager had been putting the bad light bulbs that he'd removed back in the package (A19 lamps---the old days).
I had to drive to the local Safeway, spend 99 cents for 2 new incandescent lamps as I hadn't brought any with me, and...well you get the picture.
How many electricians does it take to screw in a lightbulb?? Just one, but it can be quite costly if he's on double time