Comment by francogt

Math. I majored in psychology (very little math relative to STEM) and got into programming after graduating. After 5 years of working as an ML engineer (basically a lot of calculus and linear algebra) I decided to study more abstract math starting with proofs and discrete math. So many things started making sense at a deeper level and became easier. I think discrete math in particular since it’s very important in CS but just like playing an instrument, it just improves your thinking.