Good fiber.
Bad routes.
ZeroLag started with a familiar bug report: a tier-1 CS player on 1 Gbit symmetrical fiber, losing rounds to peeker’s advantage. The line tested clean. The router was fine. The ISP swore everything was nominal.
We pulled traceroutes for a week. The packets were taking the long way around — Helsinki to Frankfurt via London via Amsterdam because that’s how the transit contracts settled at 2 a.m. when the BGP tables last reconverged. The internet was doing exactly what it was designed to do, and it was wrecking his ping.
The public internet routes for cost and reachability. It does not route for latency. If you play competitively, that distinction is the whole game.