A fun activity if you’re a Googler is to go read ancient design docs, like the original pitch for bigtable. They are pretty short for the most part, and they were written by the legends. These are the Federalist Papers of your company, they give real context to how the company arrived here. In particular I always enjoyed reading the jarring parts were they describe something that definitely did not make it into the implementation, or got removed later. It’s interesting to think about why they considered those things important enough to write down at the time.

Now that I wrote the above, it's a bit sad that there aren't many design docs for open source software, even ones that originated from companies with good design doc culture. Where's a doc that discusses alternatives considered and rejected for kubernetes or grpc?