... security policies changing (shoes on or off?), repeated "ATTENTION, BY IMMEDIATE ORDER OF THE TSA" announcements, people doing dumb things, people being rude, baggage getting lost, flights being overbooked...
There's a lot.
Most of the time it works out, but that was the point of the observation: most can still be pretty stressful.
One way to make the airlines care more about your luggage and make it highly unlikely for them to lose it is to check a firearm as described in Deviant Ollam's famous talk on the subject: https://www.youtube.com/watch?v=KfqtYfaILHw
There's a lot.
Most of the time it works out, but that was the point of the observation: most can still be pretty stressful.