Errickfoxy said:
I think you mean Chekhov's gun.
Anton Chekhov said:
Remove everything that has no relevance to the story. If you say in the first chapter that there is a rifle hanging on the wall, in the second or third chapter it absolutely must go off. If it's not going to be fired, it shouldn't be hanging there.
That and Conservation of Detail. If the asthma inhaler has nothing to do with the story, you don't show it, because it's an extraneous detail. I feel Chekov's Gun is more about showing something early so when it does become important later it doesn't seem like it came out of nowhere. Though there's a fair bit of overlap there.
The trouble is that these should not be taken as absolutes. See here [http://www.giantitp.com/articles/YUMiX2JPVjHIJ6h5VlD.html], for example. In some cases adding plenty of extra details can actually be extremely important. That article is about roleplaying games, but it's applicable in lots of other areas. Take a murder mystery, for example. If you don't fill the world with lots of details to mislead both the audience and your characters, there can be no mystery at all.
Even in other stories and genres, background detail can often be a good way of just setting the tone or giving things a bit more character. That gun hanging on the wall might be mentioned simply to let the audience know that the person who lives there is the sort of person who has a gun hanging on the wall; maybe a hunter or a retired soldier or something. The gun itself could be completely irrelevant and never mentioned again, but the world and characters are that little bit more fleshed out because of its presence.
When it comes down to it, Chekhov was simply wrong to say that the gun should not be there if it's not going to be used. The overall idea of conservation of detail is not a bad one, but it's not something that should be adhered as an unarguable dogma. You don't want to flood your works with unnecessary details that just confuse your audience and get in the way of the important parts, but neither do you want to remove all extraneous detail to leave a dead, flavourless world with the characters simply jumping from plot point to plot point.