This is one of the most common questions I get regarding the Commenting Policy, and although sometimes it's from a butthole who knows damn well why their comment was deleted and just wants to be a further pain in the keester, more often it's from a commenter who is genuinely inquiring in good faith why their comment was deleted so they can make sure they don't make the same mistake again.
And I don't mind answering those emails, but I don't always have time to answer them as promptly as I'd like, so, for quick reference, here are some reasons why your comment may have been deleted:
1. You left it as a reply. If Disqus allowed me to turn off that function, I would. But they don't. So we ask commenters to please refrain from using it, and instead use the @[username] method, so we can maintain flat threads to: 1. Accommodate people with visual processing disorders for whom nested threads are difficult to navigate; 2. Facilitate moderation; 3. Encourage a single, on-topic conversation in each thread.
Side Note: Why is an on-topic conversation important? Because the contributors here are human beings, each with our own set of sensitivities and triggers. We write what we are prepared, on that day, given what emotional resources we have (or don't have), to discuss and moderate. If someone introduces something off-topic that we're not prepared to navigate, it can take a toll on us personally.
I understand why it is that you would want to discuss some difficult topical item at Shakesville, because you value being able to discuss things with the protection of our vigilant moderation, but please remember that that vigilant moderation is provided by people—people who live lives outside of this space, including me. I don't report everything that happens in my day-to-day life here, and, like everyone else, there are days where things in my private life are emotionally draining. I write about what I have the ability to deal with that day. So do the other contributors. That's why we want to keep things on-topic.
(There's also the possibility I haven't heard about it yet. In which case, the best thing to do with potentially triggering information is to email me or DM me on Twitter, which gives me the opportunity to process it and introduce it in my space when I'm best prepared, as opposed to dropping it directly into comments, which obliges an immediate response.)
And there's always the Open Thread for general discussion, if there's not a dedicated thread for something you'd like to discuss with other members of the community.
2. Its content violated the Commenting Policy in some way.
3. You included potentially triggering material, but failed to include a content note. Often, one of the moderators will simply add a content note, but if we don't have time, or, frankly, if you're a repeat offender, we may simply delete it instead.
4. It included a GIF or a video. (See yesterday's update to the Commenting Policy.)
5. It's off-topic and/or derailing.
6. It's marginally on-topic, but contains material that we know, via long experience, will invite a conversation that derails the thread. This is exceedingly rare, and usually when I have to delete a comment for this reason, I will take the time to email the commenter and explain why their comment was deleted.
7. You left a comment that contradicted in-thread moderation, i.e. mods having drawn a line under a discussion that's turning into a flamewar or starting to derail the thread.
8. You offered unsolicited advice to another commenter. This also includes telling other commenters how to vote.
9. You are sockpuppeting or in some way doing an end run around the moderation.
10. You're talking trash about another blog/blogger. (Distinct, of course, from legitimate criticism of someone else's work.) I don't like it when I see conversations like that about me/Shakesville in other spaces, so I don't want to host that sort of thing here.
11. Your comment was a response to someone who was trolling. We genuinely appreciate the pushback when none of us sees a mess quickly, but sometimes clean-up requires just deleting the entire exchange.
12. You are a spambot.
We delete a tiny fraction of comments left in this space, and the moderation team constantly converses about moderation decisions and collectively determines the best way to deal with problematic comments. But deleting is something we have to do occasionally, so I hope this will help if you have questions.