Assuming that you are still learning and you learn from new experiences or concepts, what was the most mind blowing concept you learnt that totally changed how you approached programming problems?
Edit: Provide pointers to where others can learn about those concepts
The gist of it: you program procedurally without thinking too much about the code and only add "compressions" when the need for them arises. The compressions can take various forms like encapsulating data types within objects, behaviour within functions, extracting often-repeated operations into separate libraries and then loading and referencing them when needed, etc.
[1]: https://caseymuratori.com/blog_0015