Despite the enormous welling up of sentimental joy I feel whenever QBasic is mentioned, on a more professional note I still find it incredible when I meet a programmer that goes through their days without breakpoints, or an interactive debugger, or a REPL/immediate window to try stuff out, or the ability to jump to the definition or docs (in hypertext!) of a function. Heck, I know some R programmers that don't even know they're allowed to write their own functions.