At a former employer someone created a framework to try and create a generic process to process and load data (i.e. ETL). It was written with the best of intentions, but was terrible.

This framework was given to an offshore team, and they were told to use it to farm out hundreds of requests. The framework was inflexible enough that they each started adding snippets here and there to make it work for those projects, with no code review.

When I joined there were well over a hundred different projects, all using this framework at the core, most having little bespoke tweaks to make the code work. Every failure was essentially a new failure in a new way.

It was a useful experience - it's one of those experiences that teaches me via a negative example. This was the worst example of how "roll your own" resulted in incredible technical debt I've seen.