(Quasi-spoilers here for all three Zones books, in that if you've got this idea in your head as you read, some plot twists will be obvious ahead of time.)
I recently read Vernor Vinge's Children of the Sky, and it reminded me all over again that all three of the Zones books have a running trope/subtheme about what happens when all of your data about reality is corrupted.
This is more explicit in A Deepness in the Sky than in the other two books; in Deepness, there are some characters for whom pretty much all of their information about some aspects of reality is coming to them through channels controlled by, and alterable by, bad guys. If you control all the data someone is receiving, then you control their perceptions; in effect, you control their model of reality. Back when I read that book and noticed this idea, I summarized the idea as control over communications is control over reality.
But the version of this idea in Deepness requires vast technological resources, whereas in other contexts it may not require any technology at all. Even though the technological aspects vary, the concept crops up over and over in all three of the Zones books.
It can happen in real life, too. I was fascinating by the claim in a 2009 Time article that Cheney was feeding ideas to Bush through roundabout routes; that he was acting as a “sounding board for advice he originated himself.”
And I think on a smaller and less intentional scale, it can happen to any of us if our sources of input or information or advice become too limited. If the only books you read during the Bush presidency were conspiracy theories about fascists taking over the US, then of course you would be scared. Likewise if the only news you watch is Fox News, or if the only person you talk with is your SO. Your perceptions are shaped by the information you get; if all of that information comes from a false or biased or even just limited source, or narrow range of interconnected sources, then your mental model of reality will be shaped by what you're hearing.
But aside from any Big Philosophical Issues, I think it's interesting that this idea is such a strong recurring thread in the Zones books. I don't recall it being so prominent in most of Vinge's other work (though it's been a while), and although it certainly comes up in plenty of fiction (if nothing else, in the form of the basic question of whether someone who's telling a character (or the reader!) something is lying), I don't feel like this particular formulation of it is all that common. But then again, it may be seeming more prominent to me in these books than it really is; I'm looking at them through the filter of this idea.
(Another entry written in early 2013 but not posted 'til now.)
(See also Facebook thread for this post.)