1. More of a CompSci aha: Hard problems are hard. Sometimes I get frustrated over getting stuck in a bad local optimum that I can't easily get out of. But then if I take a step back, I notice that the problem is NP-hard, that I'm not gonna solve it by throwing random heuristics at it and I need to either change the constraints to make it P, lower the input size, or lower my expectations. Simplest example: Deciding what goes in which shelf in my home is NP-hard. Solution: Get rid of stuff more liberally -> (n' < n) -> f(n') is much easier than f(n)

2. Doing NAND to Tetris the first time. It taught me not only how computers work, but how powerful recursive layers of abstraction can be. I had absolutely no idea how my system looked on RTL, but I was still able to build it.

3. Also Lisp. I wish Nand to Tetris had picked something more lisp like in the second half to show how simple and powerful it is.

4. When I'm just coding something- alternating writing and testing - is much quicker than writing a bunch and then debugging it. For bigger projects, setting up CI/CD early can similarly save headaches.

5. The functional big three (map, filter, reduce), but for me even more so closures. I had gotten stuck trying to hardcode coefficients for a polynomial until I noticed I'd end up with a lot of duplicate code, which was what I was trying to avoid with FP in the first place. Then I realized I could just put the polynomial function itself in a closure and call it with the coefficients I wanted, when I wanted.