It took me a bit of thinking to decide on an experience that has changed how I play the game. After some thought, I will say that for me it was not an in game Experience that changed how I play the game. It happened to me as I was reading new system.
That system would be Monte Cook’s Numenera. For me, up until this point of gaming. I had never thought about not rolling any dice as a DM. Additionally, I was entirely floored by the simplicity and elegance of the system as a whole.
After reading this book and the following bestiary. The idea of making my life as a DM easier not harder became a motto for me in all my games. It sent me on a quest to amass any and all tools that I could use during games to allow me to focus all of my energy on running the game not “managing the game”
I know it was not the first to do this but for me, it was the first to open my eyes to the concept.