[insumanth]

The line that stuck with me: "Recovery after congestion collapse is an uncommon regime, but it is exactly the regime a congestion controller exists to handle." This generalizes well beyond congestion control.

Most control loops have the same property. The path the system follows 99% of the time gets well-exercised; the path it falls into when things go wrong is the path you actually need to be correct on. There's usually no way to discover the bug until you deliberately drive the system into the bad regime and watch it try to climb out.