For me, the blue Smalltalk book by Adele Goldberg was deeply formative. It was computing done right and from first principles.

The other two formative experiences for me were using Cincom’s Mantis on the 3278 and Dataflex 2. Both made it obvious how quickly one could go from screen to persisted data, CRUD, application logic, and reporting with the right level of abstraction. Much later I described Dataflex as “Rails for the VT100”. Sadly, Cincom will not provide a hobby license to run it on an emulated 4381, and won’t even give away free manuals, and the company behind Dataflex (I don’t remember their name right now) seems to not even have any versions from that time. When I read Paul Graham’s Beating the Averages, it all clicked perfectly.