I just finished the first part of Jon Peterson's new book last night. One of the things it really hammers home is both how dire the straits were for Gygax, and how unexpected the success of D&D was in the overall context of the hobby.
I think it is easy to see, now, especially with video games having aped the model, that the play model of D&D is crucial to the success. But I still think we often forget how crucial it is to the success of D&D vis-a-vis the TTRPG market. To put it in simple terms- one reason that D&D succeed, where branded TTRPGs (Dr. Who, Star Trek, etc.) do not do as well, is because of this leveling loop that is crucial to the long-term interest. As much fun as it is to be your Kirk (or Picard, or Sisko, etc.), you want that reward mechanism.
Sometimes the obvious needs to be pointed out.
(I have to admit that I feel like I can't win with certain commenters- either they pick apart a single sentence in a giant essay I write because I'm wrong wrong wrong, or they chime in to complain that I shouldn't bother writing about something so obvious. I guess they want a refund of the money they paid me?

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