Big-endian Support for AMD64 - the explanation from the person in the crowd is something of a horror story that I think a lot of have witnessed in various forms.

https://youtu.be/GnBbhXBDmwU?t=2330

I seem to recall him giving a live feed of his findings while spelunking into the codebase.

I think I actually got grey hairs from that...

Then I realised that OpenSSL is quite entrenched, I'm still running it to this day, in production.