When you write something, you HAVE to know more than your readers. You HAVE to have a backstory, even if it's a backstory that you never intend to tell your readers. You have to know exactly what everyone's goals are, and why everyone does what they do. Also you have to know who's lying, who's telling the truth, who's just clueless, and why. You have to know if Mulder's sister is alive or dead, or a clone or an alien hybrid, or just on vacation in the Bermuda Triangle. You can't be so arbitrary as to change your mind week after week. There shouldn't be 5 different stories with 5 different people absolutely convinced that their story is correct. You absolutely never have to tell your audience what is true, but if you tell a completely different contradictory story every few episodes, then you start to anger people. Don't get me wrong, it's ok to have twists, to mislead your viewer/reader. But YOU had better know what's really going on or it's going to be a jumbled mess. And the X-Files far too often felt like an inconsistent jumbled mess. Secrets and mysteries can be good. But you have to keep the story going and make the audience feel like the story is progressing, that they are figuring things out along with the characters even if you have the occasional misstep or mistake. But there was nothing to figure out in the X-Files mythology because everything felt so arbitrary. Nothing you figured out was ever 'True' with a capital 'T'. Each episode had its own truth that had absolutely nothing to do with the overarching story, since it would be completely ignored in the very next episode. There were aboslutely some riveting episodes. But that mythology and overarching plot was just a mess.