20+ years ago we got a contract to replace an old home grown system for managing rented equipment for a company with offices in two countries with a new standard system.

I was tasked with building a few addon modules to handle import and reporting that the standard system lacked.

Over the course of 8 months and multiple trips to their head office for on premises development along side their people that knew how it should work (there was a lot of waiting for info so it was not 8 months of actual work) we finally was ready to present the finished solution.

After about one hour of demonstration their boss questioned why we did not demonstrate the connection to their corporate group accounting system ...

“Corporate group accounting?”

After some confused discussion it turns out that in one of the first meetings the sales person had they had mentioned this accounting system and that all accounting info was to be exported there.

This requirement was never listed in the specifications we got and looking into it it turned out that the standard system did not support such exports at all.

In the end we had to throw it all away as it proved impossible to get that info out of the system (which was not of our design).

We barely avoided having to repay all fees as their people had approved the specification but standing there without a clue to what he was asking for was a very scary experience, thinking “how could we miss this?”