As is often the case, another illustrative example is Nethack. After completing the weeks or months or years of ramping up to being able to ascend a character and complete the game, the higher levels of play are ALL ABOUT the "voluntary conducts", many of which have subsequently become recognised by the game. Can you complete the game without welding any weapon? Without using any magic (being illiterate?) While being vegan? Without eating any food? There are dozens of these, each of which requires extensive modifications to a players style, morphing the gameplay.