This is all pretty standard electronics design these days. If you're interested to learn more, you can search for "differential signaling".

What it comes down to is that once your signal rate is high enough, the speed that electrons move becomes a concern. Matching the length of your traces ensures that a signal sent down two wires at the same time arrives at the same time.

That's the general idea anyway. This topic gets very complex the further down you go

> What it comes down to is that once your signal rate is high enough, the speed that electrons move becomes a concern.

To be clear-- the speed that charge moves in the cable. The actual electrons move really, really slow-- often centimeters per hour slow.

While that's true, it sounds much less exciting.

It's basic transmission line theory.

https://en.wikipedia.org/wiki/Transmission_line

The other commenters got it spot on for where you can learn more, but as to where I learned it, I decided I wanted to build a project with USB C running at 3.0 speeds and had to deep dive on the subject in order to make it work.

It was surprisingly hard to gather all of this information in one place and actually implement it given the resources on the internet a few years ago. Even then, there were still some board revisions that got it a bit wrong, one where I left out the decoupling capacitors I'd later learn were a critical detail, and one where I put all the wiggles clumped together at the middle of the shorter trace and so despite both signals arriving at the end at the correct time, they were out of phase for nearly the whole trace run and caused (presumably) cross talk between each other. But I did get it working in the end :)