One of the critical questions any creator should ask is, “Who is it for?”
For a game master creating an adventure or a campaign from scratch, the answer is easy. The people playing my game.
For the game designer creating an adventure, scenario or setting; the answer is slightly more complicated. Is the adventure for the game master or is it for the players? Both? Ultimately, I think it is for the players but it has to be in a format that excites the game master enough to want to present the material to the players.
What do they want? They want to have fun at the table but ultimately, what they want is the feeling they get when they are having a good time playing through the designer’s adventure. That’s going to be different for the particular game. The feeling players are looking for in a Call of Cthulu game is different from players of a Dungeons and Dragons or Starfinder game. The designer has to be aware of “What do they believe?” “What do they fear?” “What is important to them?” I think some of this is very hard but worth considering, at least, before getting started to write a new adventure or setting.