Today I'm going to tell a story from 1996. Why? Because I can.
One of the tests performed by Windows Hardware Quality Labs (WHQL) was the NCT packet stress test which had the nickname "Hell". The purpose of the test was to flood a network card with an insane number of packets, in order to see how it handled extreme conditions. It uncovered packet-dropping bugs, timing problems, all sorts of great stuff. Network card vendors used it to determine what size internal hardware buffers should be in order to cover "all reasonable network traffic scenarios".
It so happened that at the time this test had currency (1996 era), the traffic on the Microsoft corporate network was approximately 1.7 times worse than the NCT packet stress test. A card could pass the Hell test with flying colors, yet drop 90% of its packets when installed on a computer at Microsoft because the card simply couldn't keep up with the traffic.
The open secret among network card vendors was, "If you want your card to work with Windows, submit one card to WHQL and send another to a developer on the Windows team."
(This rule applied to hardware other than network cards. I was "gifted" a sound card from a major manufacturer and installed it on my main machine. It wasn't long before I found and fixed a crashing bug in their driver.)
[Raymond is currently on vacation; this message was pre-recorded.]