For me it was realizing what autorun.inf is for, from that realizing some programs load texts and images off the same CD they came with and I can change those a

For me it was realizing what autorun.inf is for, from that realizing some programs load texts and images off the same CD they came with and I can change those and change the program that way, then I discovered a few programs built around displaying unbundled HTML files and that I could change those in Notepad leading to the discovery of HTML and later JavaScript and by that point I was too far gone. So not exactly games, but these CDs and programs I was messing with were shareware CDs and their launchers so still kind of a +1 for games.