Nothing has had more impact on the way I see games than The Forge. Sorcerer brought me there.
Moreover, trying to wrap my head around how to run Sorcerer was a 15-year quest of improving my skills in one area, only to realize I had so much further to go. When I finally ran a session of Sorcerer that went well, it felt as if I had finally internalized so many lessons from so many games. Yet, I found myself reconnected with first principles of RPGs, just from a different perspective.