I have found that 99% of all network problems are bad wires.

I remember that the IT guys at my old company, used to immediately throw out every ethernet cable, and replace them with ones right out of the bag; first thing.

But these ships tend to be houses of cards. They are not taken care of properly, and run on a shoestring budget. Many of them look like floating wrecks.

If I see a RJ45 plug with a broken locking thingie, or bare wires (not just bare copper - any internal wire), I chop the plug off.

If I come across a CATx (solid core) cable being used as a really long patch lead then I lose my shit or perhaps get a backbox and face plate and modules out along with a POST tool.

I don't look after floating fires.

I recently had a home network outage. The last thing I tested was the in-wall wiring because I just didn't think that would be the cause. It was. Wiring fails!

If I had a nickle for every time someone clobbered some critical connectivity with an ill-advised switch configuration I wouldn't have to work for a living.

And the physical layer issues I do see are related to ham fisted people doing unrelated work in the cage.

Actual failures are pretty damn rare.