One thing that people do sometimes is that they self-boost toots that were unlisted (e.g. because they were deep in a reply chain under something unlisted), so that they appear once in the public timeline (and/or on their "toots" list instead of only "toots and replies").
("Unlisted" means technically that as:Public is not in the `to` field, but in the `cc` field.)
@robryk Oh yeah, but the context I was seeing is the same toot coming over and over to the top of my timeline after I'd already read it because it was important to the writer. It doesn't impress itself in my brain more on the fifth viewing; I've already read it.