system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does an internet connection become slow?
gpt
Lots of things can have an effect. If many people in your home are using the same WiFi network, the network may become bogged down. Interference can seriously degrade your signal, if there are any big sources of interference between you and the router. Walls, floors, etc can have an effect on wireless signal too. 

A wired OR wireless connection may be throttled by your provider or slowed down if there is a lot of internet traffic in your area.

Outdated modems/routers or damaged equipment (modem, router, Ethernet cables, antennae, cable in the ground) will certainly not help.