Beyond that, the UX of this is always subverted by incentives.
The system's incentive: (1) make sure no pass is used to board more than once, (2) indicate whether all ticketed passengers have boarded, and if not which are missing
The gate agent's incentive: (1) board everyone as pleasantly and quickly as possible
So the errant boarder played on the misaligned incentives and time pressure, to bet that the gate agent would ignore any errors.
I'm incredibly distrustful of any system that requires:
- Someone deal with a rare situation
- In realtime
- Under pressure
- While not being incentivized against an adverse outcome
"Well, the person didn't do what they were supposed to in the 1-in-1,000,000 situation" isn't a valid design strategy. (See self-driving-car-interventions and TSA agents)
They are being incentivized against an adverse outcome: the outcome of a paying passenger (or a whole planeload of paying passengers) missing their flight, connections, etc. That's why they make the decisions they do.
Accidentally carrying a non-paying passenger on an underbooked flight is also adverse I guess but it's not the only way the system can err and it's not the only thing they are trying to avoid.
The system's incentive: (1) make sure no pass is used to board more than once, (2) indicate whether all ticketed passengers have boarded, and if not which are missing
The gate agent's incentive: (1) board everyone as pleasantly and quickly as possible
So the errant boarder played on the misaligned incentives and time pressure, to bet that the gate agent would ignore any errors.
I'm incredibly distrustful of any system that requires:
"Well, the person didn't do what they were supposed to in the 1-in-1,000,000 situation" isn't a valid design strategy. (See self-driving-car-interventions and TSA agents)