John Lloyd1
Rigidly defined areas of doubt and uncertainty
Of course D&D needs to be fun.Of course, my way is a bit different: Make a Fun Game.

But, what is fun for one person is not always fun for another. You can see that in the thousands RPGs, board games, books, media, etc. Most of them were fun for someone. None of them were fun for everyone. You can see that in the arguments between edition fans. You can see that in the arguments about what is OSR.
In a sense, they are trying to maximise total population 'fun-ness'. And, like speed of light, you will never reach 100% total 'fun-ness'.