I replaced a network cable.
Supposedly the client had checked everything, double checked everything, triple checked everything, & "done everything Humanly possible" to fix an issue for nearly a month before calling my employer for a fix.
Employer sends me out, I start checking all the physical connections first to get them out of the way, & realize that the Cat5 cable's little locking tab thingy is broken off. I replace the cable & the problem went away.
A thousand dollar multi hour plane flight to send me out, car rental to get me from the airport to the client site, a hotel reserved for me with an open-ended occupancy, and it all got fixed faster than the hire car attendant took to make sure I was legally allowed to drive a car at all.
I checked in to the hotel, informed the manager that I'd need it overnight, requested a wake up call for my return flight in the morning, called the airline to let them know I'd need to be on the return flight in the morning, and set about to enjoy a nice meal (room service) & use the room internet connection to chat with my girlfriend at the time.
Next day goes without incident, I get back home, & report to work the next morning as normal.
Boss nearly has a cow when I tell him what happened & how long it took to fix. He demanded to know why I used the hotel & spent the night if I could have been on a flight back the same day.
"Because if I *had*, I wouldn't have arrived until after close of business & been one very grumpy boy when I showed up this morning. Instead I spent the night in a hotel you had already paid for, had a meal within my meal allowance, took a leisurely flight back, had a good night's sleep to lose the jetlag, & am fully prepared to get to work right now *without* ripping off anyone's head for intercepting me before my first tankard of caffeine."
Boss gave one of those sheepish full-toothed grins as if to say "Ok, please don't kill me" and let me go. My meal was part of the room cost, so I didn't even have a receipt to hand over to the bean counters for reimbursement, thus it all ended fairly calmly.
Sometimes you wish you could reach through the phone & thwap the caller in the forehead while shouting "WAKE UP, DINGUS!" in the hopes they congeal enough coherency to realize that they could save themselves a hefty bill & the responding on-site tech a LOT of headache meds if they just, y'know, ACTUALLY did some basic checks before calling... /Sigh/