In the course of reading submissions for an anthology, I received a story. No big deal. Well-written, but ... Well, let's say for the sake or argument that I was looking for three particular things in every story. A theme, a kind of content, and a kind of tone. The guidelines were very clear about this. And this story failed on 2 1/2 of those criteria. It lacked everything I said I wanted, even if I was being generous. So I rejected it.
"But Michael," you say, "that's pretty much a normal thing for the slush pile. People don't get it. They don't read guidelines. You chuck them out the door and move to the next one."
Yes, that's what you do. I rejected the story and that was that. Until the author wrote me back to thank me for the reply ... and said "No harm in trying."
No harm? I suppose not. No real harm. I'm not going to burn down your house for a bad story, or blacklist you, or have your dog kidnapped and sent to Siberia. No one suffered injury, the world didn't slow down for even a second, and that black hole's no closer to swallowing us all. But mark my words, there was harm. Potential harm to your career.
Editors remember these things. This author will forever more be "That guy who sent me a story that was utterly incompatible with my needs because he didn't really care about the guidelines, suitability, or market." I might not remember him specifically, but the name will likely ring a bell if it turns up again.
Editors talk. We're only human, we gossip about the good, the bad, and the spectacular flame-outs. How many times do you pull this sort of thing before you get a rep as "The guy who flings trunk stories at any market that stands still, but doesn't know how to read guidelines, and doesn't care?"
Editors get around. Sooner or later, you'll end up doing this to an editor, who might move into a position where you need that goodwill, and it'll be lacking. Say goodbye to that market for your first novel.
"But Michael," you say, "these are all worst case scenarios, and certainly you're exaggerating and over-blowing it."
Perhaps so. But still, dear author, don't be that guy. Don't be the one who fails at meeting every single criteria laid out on the guidelines. Or I'll mock you again. In French.