Human error happens with much greater frequency in aviation than you might believe - I have experienced some absolutely hair-raising moments (watched Lufthansa lose a winglet on landing while the stewardess prayed, had an aerolinias argentinas flight take off with a luggage compartment still open, and a air Bishkek flight where the wheels locked on landing and we ground down the runway at sheremetyevo on hubs), and have been told tales of others by pilots that I wish I hadn’t been told.
The thing is, most of the time, it’s nothing more than some scared passengers and a messed up schedule. “Almost” didn’t happen.