Also, much like some people are Excel wizards, some people were Apple II monitor/mini-assembler wizards or MS-DOS DEBUG wizards, or whatever other thing already

Also, much like some people are Excel wizards, some people were Apple II monitor/mini-assembler wizards or MS-DOS DEBUG wizards, or whatever other thing already lived natively on the machine. If someone has strong knowledge of the machine, a handful of carefully targeted little software augmentations, and well-developed muscle memory for the commands, watching them use a debugger/monitor can be almost like watching someone use a REPL.