How the Two Generals problem caused a massive food delivery service screw up

One night in September 2018 the food delivery service Deliveroo went haywire. It sent some customers the same food order several times, and other customers got nothing. In this video, Tom Scott explains that this was a classic example of the "Two Generals" problem, and how Deliveroo's "Night of the Multiple Orders" could have been mitigated -- by using something called an "idempotency token," which allows a transaction to only happen once.

Image: YouTube/Tom Scott