The mental debugger is definitely one of the tools I'm glad I developed early. For me, it was by reverse engineering. I started cracking software and eventuall

The mental debugger is definitely one of the tools I'm glad I developed early. For me, it was by reverse engineering. I started cracking software and eventually moved on to white-hat black box security auditing, and that quickly taught me how to evaluate execution flow mentally. I find that even though I'm writing high-level Ruby web apps now, my ability to rapidly follow code around in my head lets me debug more quickly and effectively than many of my co-workers. I firmly recommend trying reverse-engineering for anyone who hasn't - it will forcibly provide a lot of the same metal execution mapping abilities while feeling more relevant than writing machine code or assembler out on a piece of paper. And once you learn the basics, everything transfers back up to higher-level languages pretty well (with the exception of mental hex arithmetic, which will still come in handy as soon as you segfault your high-level language's runtime). Plus, when reverse-engineering, you can't fall back or get frustrated and use a compiler - unless you have an IDA + HexRays license for some reason, you're stuck figuring things out yourself. As a side-note, it's always fun watching my dad work - he's an oldschool mainframe guy and he'll sometimes solve common setup issues using JCL or REXX stuff with a modified date sometime in the late 1980s.