[poppingtonic]

Reading textbooks.

Using a REPL-based language like Lisp (which I learned from reading advanced Lisp textbooks) for several years before I worked professionally as a programmer enabled me to dive into complex, underexplored parts of the (Python, C) projects at my first job, which meant I basically owned some very important parts of the stack.

Reading and applying ideas from Unix sysadmin books enabled me to be comfortable jumping around the OS very quickly, giving me a speed advantage even when the computer I used was pretty underpowered, relative to my colleagues, early in my first job.