My Ethernet connection was running at a fraction of its rated speed, and the problem wasn't my router

Whenever I'm having trouble with my internet connection, especially speed- or latency-related issues, the first thing I usually do is restart my router. If that doesn't work, I'm quick to blame its aging hardware or complain to my ISP because what else could realistically be the problem? So when I noticed my Steam downloads struggling to break 100Mbps despite having a 500Mbps fiber connection, I started wondering whether it was time to ditch the D-Link DIR-882 that I've had for eight years.