When you’re writing in a fictional world your readers do not know, you can get away with making a lot of stuff up. A colony on Planet Saturn in the year 2072? No problem. Wing it. Who’s going to know the difference?
The place you can’t get away with just making stuff up is in non-fictitious worlds your readers do know – and know well. For example, Hollywood or the New York publishing world.
This trips up a lot of beginning writers who write protagonists who are successful authors or successful Hollywood players. (Do not ask me why, new writers are compelled by some law of physics to as some point early in the career write a successful writer character. It’s like animation artists being compelled to as some point animate an evolution sequence. Everyone has to do it at least once and no one knows why.)
If you don’t intimately know the inner workings of the film industry, the publishing industry, or the locations New York or Los Angeles, and try to set a story in these worlds, this is going to kill you dead when you try to fake it because people in the film industry and publishing industry know these worlds intimately and every error you make “winging it” will stand out like a neon red elephant standing ankle deep in a kiddie wading pool.