I realize that "overbook" can mean different things but United flight #3411 wasn't oversold to statistically offset no-shows. Instead, the plane had a capacity of 70 seats[1] and United sold all 70 seats to paying customers with zero cancellations. That's a perfect economic situation for United.
What went wrong was 4 extra United employees needed a last-minute ride on that plane to Kentucky. Since this is an HN audience, I guess we could frame it as a massive failure in the "information flow" through their computer reservations system.
The very second that United knew they had 4 employees they had to acccomodate, their computer system should have immediately confirmed those 4 employees on flight #3411 first such that the plane only shows 66 available seats instead of 70. (Computers doing math for the win!) That way, either 4 of the customers get denied a boarding pass at the check-in kiosk, or they get denied at the gate that scans the barcode before they enter the jetway. Instead, United let all 70 passengers board and settle in their seats.
If United insists that their employees take precedence over paying passengers, their damn computer systems need to reflect that reality in the seating database!
All of those opportunities to have the computer system "help" were missed that would have prevented the situation from escalating to a bloody face plastered all over the news.
[1] https://www.seatguru.com/airlines/United_Airlines/United_Air...