I previously said that in media where the audience is relatively passive such as books and movies, the writer (and in the case of films, the director as well) can keep the audience from asking rational or scientific questions that would undermine the fantasy. In the Star Wars, Lucas slipped up, however. When he introduced midichlorians as the biological basis for the force, he opened a can of worms (see
here). As a movie-maker, he was able to minimise the damage by not revisiting them in the subsequent Star Wars films. But as a GM in an RPG, they're even more problematic. What is to stop a PC from investigating midicholrians with a vue to creating a biological agent that counters them thereby neutralising someone's use of the force. And if the force has a scientific basis, then shouldn't force effects have them too? Why can't force effects be investigated scientifically as well? By introducing a pseudo-scientific explanation (midicholrians) for a supernatural effect (the force), the integrity of the fantasy elements is jeopardised.