My first job was at a large telco equipment manufacturer, testing on their main digital switch. Fresh from school it was quite impressive, people sitting at testbenches full of phones, between racks full of blinking lights, all looking at hexdumps and patching assembly straight into memory (really!).
After some time I got the offer to work on a kind of "black project", which basically involved moving part of the ancient embedded Pascal code out of the system on to a modern Unix server in C++ to speed up processing of this specific part. I knew C++ and had some basic knowledge of Unix, but I had to learn socket programming and threads from scratch. The upside was that being it a black project there were no firm deadlines and with two people working on it (the other guy transforming the old code, me doing the server part) I had a lot of fun figuring it all out.
After some basic succes the interest grew, so some more modules were added and some people were called in to help. During one of the planning meetings we explained some intentions to one of the old-school embedded developers, still working on the switch. We needed some modification in the home-grown database, for which we would use two of the spare bits present in one of the fields. We were happy there were still some of these unused bit, because otherwise the datamodel had to be adapted and that would have taken three full developer weeks to get it done, which was definitely not allowed at that moment. The dev didn't share our hapiness though and kept saying we had to modify it anyway. When we asked why, he said "If you use those spare bits, we need to add new ones, because the old ones will be gone!". If we asked what for, he said you can't just use spare bits, you need to add them again!
It took 5 people more than 1 hour to convince him that those spares were there to be used for just that kind of cases that we had. At the end he still didn't believe it, but he executed it anyway. He was one of the main developers of this flagship switch, I still wonder how they got that one running so well...