(You should note that delusions represent a small, pathologic subset of false beliefs, really a disturbed belief process distorted by different anatomy. We all have false beliefs, but hopefully we can update them when we get new information. Even when people don't update their beliefs based on relevant information - they're usually identity-forming or socially important beliefs - and frustrating though that is, that is still different than a delusion. So, no, your most un-favorite religion or political party adherents are not delusional, even if they're wrong.)
There are a number of misconceptions, or more accurately, misexpectations, that I had about delusions when I went into this business, which will be glaringly basic and obvious to any psychiatrist, but will probably not be so obvious to other people. In no particular order:
- If and when delusions resolve, there is only rarely a "eureka" moment where the patient realizes the belief is false, or has even a significant enough increase in insight to gradually look back and sheepishly say "Yeah, I guess that wasn't true." Rather than updating the belief, people just stop being so motivated by it. That is to say, in the large majority of people, rather than the belief changing, the centrality of the belief changes. I find this very unsatisfying. "Yeah, I still think drones are probably following me everywhere but I don't worry about it that much." This isn't all that much different from belief in health - confirmation bias is all-pervasive, and recall that science advances one funeral at a time.
- Related: you can't talk someone out of a delusion. Ever. (As the rationalist proverb goes, you can't reason someone out of a position that they didn't reason themselves into.) At best, you will waste your and their time, and at worst, you will anger them and damage your therapeutic alliance. And if the psychiatrist who gives into this urge is completely honest, it's partly informed by a need to "win" the discussion. Even if you know this intellectually, early in your career it's very difficult to avoid engaging a delusional patient in this way (partly because the patient will not infrequently challenge you to do exactly that.) At this point I'm proud to say I can mostly resist the temptation.
- Though delusions sometimes do appear in isolation, they rarely occur without other neuropsychiatric symptoms. Even delusional disorder (where the patient has ONLY delusions) is often a misdiagnosis that evolves to something else - like dementia, especially when appearing in middle age or later, with the delusion merely as the earliest symptom. So very often, the person with a delusion is quite psychiatrically ill in many ways that make having a coherent discussion about the delusion (to hear a coherent set of delusional beliefs) very unlikely; e.g., severe paranoia that keeps them from talking to you about the details of the delusion, and/or constant hallucinations which distract them and to which they respond, or merely an inability to speak in a way that makes sense at all.
- This one was most disappointing to me: delusions are rarely coherent, in contrast to how they are often presented in the lay media - for example, K-PAX, or the analysand in the essay The Jet-Propelled Couch (who supposedly was in reality the science fiction writer Cordwainer Smith.) They are sometimes completely bizarre and incomprehensible, and even after giving the patient a chance to explain, you still have no idea what they mean. (This is one subtle feature of thought and speech in psychosis: though the sentences might be grammatical and seem to be meaningful, strung together, you can't make sense of what they're saying or even clearly remember it ten minutes later - much like, I think not coincidentally, we struggle to remember an early morning dream even until lunchtime.) Even when delusions are "about" something comprehensive, they are only peripherally about discrete objective facts, delusions are based on affect and "primitive" themes of the sort that color nightmares - pursuit, certain people being morally bad, looming organizations with sinister intent, an overwhelming sense of contamination, etc.
- It is often striking how incurious delusional people are about their predicament - after years of, say, harassment by a sinister government agency, when one asks "Do you know why they're doing this? And where they get all these resources? And how their technology operates?" people often do little more than shrug. They are also usually obviously and badly internally inconsistent, again unlike the cleverly constructed delusions in fiction. If the psychiatrist in the Terminator thought the future-warrior's tale was a delusion, he was right to be impressed by it. People will tell you (for example) that they were victimized for many years by their persecutors, until they developed their special powers at age 23 that made them immune; then in the next sentence, tell you how they were victimized at 26. Rather than becoming upset when such continuity problems are pointed out, they generally just wave it off as irrelevant and keep going.
Delusions are hard to treat; even so, medications can and do help people. But if you get into this business to hear fully elaborated, articulate, consistent delusions about time travel, space empires, or sinister (but interesting) experiments that shadowy government agencies are doing on us - you're going to be disappointed.
 Even in delusional "shadow syndromes" like physics crackpots or various denialists that do seem to be focused on external objective cold facts, invariably there is ranting against the Establishment and paranoia about people stealing their work, and this takes up much of the time that might otherwise in a more rational person be devoted to research or making their case.
 Regarding this incuriosity: delusions are not the only neuropsychiatric symptom where this feature appears. I'm agnostic as to whether this incuriosity is actually part of these diseases, or is just (unfortunately) the natural state of most humans. For example, hemi-neglect is a symptom usually seen after strokes, where the patient loses one half of space. I don't mean that they can't sense what's going on one side of them; they literally can't understand that that side of the universe exists, exactly like you or I can't perceive the fourth dimension.
To illustrate: these people lose not only the use of one half of their bodies, but the awareness that they exist. So they will deny that they have a left arm. And if you hold their (genuinely paralyzed) left arm up in front of them, they often confabulate ridiculously: "That's my sister's arm. She's hiding under the table." Now, if my doctor told me I had four arms, I would tell her she was a goof. But if she could consistently could keep holding two extra arms up in front of me that had roughly the shape and skin tone of my other arms and in the middle of a room where there was no chance of a trick, I would eventually have to concede that I was having perceptual difficulties and that I indeed had four arms, even if I couldn't tell how they attached to me. Probably a more common situation is that a hospitalized patient will demand to speak to the doctor at dinner, and as the doc enters their room, says angrily "They keep telling me this is a full-sized dinner, but look at this thing!" And they gesture to their plate, exactly one half of which is eaten. So, you turn the plate 180 degrees, and they grunt, and finish the other half of their dinner, now that it exists. Now, if tonight I complain to my wife that she only gave me half a serving of dinner, and she glared at me and reached over and did something I didn't understand and suddenly my plate was full again as if it had passed partway through my dimension like a sphere in Flatland, I think I would say "Whoa! You just magically produced food out of the fourth dimension! I don't understand how you did it, but could you do it again?" But that's not how people usually react, which implies there's a loss of insight or ability to update associated with this condition. It should not be missed that most neglect is left neglect (meaning, a right-sided lesion), and that one theory of delusion holds that somatic delusions can be caused by right frontal lesions, and that some sort of functional right hypofrontality is required for the lack of insight inherent to all delusions, somatic or otherwise.