Writing for the OPAJ: Familiarity and proficiency
Familiarity with game mechanics and a game's setting seems like obvious prerequisites to write an adventure. I am not saying it is not. However, it is not. Not really. It takes a brave person to write an adventure for a game and world with which they may only have passing, limited, or superficial knowledge. However, it is certainly doable. Writing a one page adventure certainly requires some skill.
