I think it would have to be machine language, assembly language, and C used to program machines at the hardware level. This was on an Atari 8-bit except C being cross compiling to M86k. In all cases I was programming to hardware interfaces video games and laser printer firmware. What it taught me was as sense of 'you can understand it all down to the metal'. That hardly seems valuable now, but what that means is that I've always had the curiosity and desire to know how things work which leads to deeper understanding in our field.
Learning recursive programming was an eye-opener because it clearly illustrated the correspondence of programming and math (proof by induction). [Dynamic programming was meh when I learned it--memoization seems a more fitting term--as I expected to be learning metaprogramming.]
The thing I wish I'd been taught or learned much earlier is functional programming. And maybe data-oriented design if that's a name of the thing that prioritizes data schema and layers operations on them. I'm always surprised by coding-first developers not able to put fields at the appropriate place considering cardinalities, or never even think that it's important to get this right.
Learning recursive programming was an eye-opener because it clearly illustrated the correspondence of programming and math (proof by induction). [Dynamic programming was meh when I learned it--memoization seems a more fitting term--as I expected to be learning metaprogramming.]
The thing I wish I'd been taught or learned much earlier is functional programming. And maybe data-oriented design if that's a name of the thing that prioritizes data schema and layers operations on them. I'm always surprised by coding-first developers not able to put fields at the appropriate place considering cardinalities, or never even think that it's important to get this right.