I can add a few...
1. Sat at Boston's Logan, waiting to board our 8am flight to MCO. We boarded a bit late...about 20 mins. We sat on the plane for a bit, then heard some god-awful noises. Told my dd that those weren't normal sounds. Back to the gate we went, and off the plane. Mechanical issues...not complaining about not using that plane! It took JB 3 hrs to get a plane to us. So, we took off at the time I should have been checking into my hotel. Had an event that I missed...figured that it started 2.5 hrs after my hotel checkin, and was right there, in my hotel, so no problem. Nope, it was an issue.
2. Most have heard this one. Flew SW from Ft Lauderdale to Providence, New Years Eve day. We were supposed to land in Providence around 2. My dh and I realized something was up when we kept flying in very wide circles, when we should have been descending into Prov. Nope, issue with the runway...a plow had hit something and we couldn't land. Had to go to Philly! My 14 y/o dd was a mess because she was now missing her first NYE boy/girl party. We had two choices. Stay overnight in Philly, with no checked bags, get an early flight out in the morning and have luggage delivered to you, or, return on the plane to FtL, get your luggage, and stay overnight and get a flight out in the morning. All the stuff we needed was is our checked bags (we were going home!!!), snd thought we could just go back to my dad's place. But, they had more company, in our place, so had to get a room close to the airport. Nasty 36 hrs.
3. The time I was already in WDW, dd and dh were flying down to join me. Dh obsessively checks flight status, so knew their JB flight was on time. In the 45 mins it took them to get to Logan, the flight was cancelled! They had to make a connection, so couldn't take the replacement flight offered...they would be 50 mins late for that connection and have to stay overnight before flying to MCO. They were offered the flight that was biarding! Said yes, and ran. A JB person went with them, got them thru security quickly, while dh is telling dd that they are probably going to be split up snd to just deal with it! They held the door for them, had found two seats together, they sat down, and they closed the door.
Stuff happens when you fly. You have to expect the unexpected. As someone else said, I'm always surprised when we leave on time, or sometimes, even early!!