After seeing that my wireless speeds were much faster than the speeds I was getting over Ethernet, I decided to invest in some new cables. I didn’t know it before, but I saw while I was changing them out that my current cables were Cat 5e. While putting my network together, I had just been grabbing whatever cables I could find in my scrap drawers. Now I have Cat 8 cables and my speeds jumped from 7MB/s to an average of over 40MB/s. It’s a much bigger improvement than I expected, especially for such a small investment.
My favorite failure was when someone used solid-core cabling for all their patch cables instead of stranded and kept bitching about how unreliable everything was.
Which, of course, it is when you use the wrong cable and it keeps breaking as you move it around.