Why do people believe in silly conspiracy theories?

I have noticed that it usually requires a particular type of personality to believe in conspiracy theories, especially the silliest ones. That's because quite often when someone believes in one such conspiracy theory it's 99.9% probable that he or she will also believe in several other conspiracy theories as well (which are usually completely unrelated, without any connection to each other).

As an example, I don't remember ever knowing, seeing, or reading about someone who strongly believes in the Moon landing hoax conspiracy theory who at the same time does not believe in and can present strong counter-arguments to the 9/11 terrorist attacks conspiracy theory. Or the other way around. There may be such people, but they seem to be very rare.

By far one of the silliest conspiracy theories in existence, which a scary amount of people appear to believe in, is that the Earth is flat. They honestly seem to believe that literally millions of people, including scientists, engineers, airplane manufacturers, pilots, seaship captains, cartographers, satellite and GPS manufacturers, as well as thousands and thousands of companies, corporations, governments, military personnel and so on and so forth, from all around the world, from different countries, cultures, customs, beliefs, belief systems, are all knowledgeable of the fact that the Earth is actually flat but are in a huge world-wide conspiracy to hide it. They literally believe that military forces, using thousands and thousands of military ships, are patrolling the tens and tens of thousands of miles of the Antarctic ice wall that surrounds the world, stopping anybody from going there (even though nobody has ever seen these ships).

And it's not always about intelligence. Perhaps all flat Earth conspiracy theorists are bumbling morons with an IQ in the 50's, but I know people who are quite smart and capable who still believe in the other "less silly" conspiracy theories, and believe in them so strongly that no amount of counter-arguments or evidence of the contrary will persuade them, no matter what.

(One particularly devious characteristic of an actually smart and intelligent conspiracy theorist is that he can sometimes "ambush" you with an argument or piece of "evidence" that you have never heard of and which you may have difficult time explaining on the spot. That's because these people tend to have read miles and miles of documents and web pages, and watched tens if not hundreds of hours of video material, and thus can know literally hundreds and hundreds of "evidence" for the conspiracy theory, and if smart enough, can choose a more unusual one and "ambush" you with it, catch you by surprise if you have never heard of it, and make it difficult to give an explanation on the spot. And, of course, they immediately jump to "you can't explain this, therefore you are wrong", even if just implied. Of course if you later do some research on that particular argument you'll find out that it's usually presented in a very misleading manner, usually a form of visual or argumentative deception. It's like a magic trick: When you don't know how it's done it's very convincing, but once you know how it's done you see the deception, the trickery, the real explanation behind the scenes. Smart conspiracy theorists are like magicians: They will fool you with tricks, and if you don't know how they are done, you'll struggle for an explanation.)

But why do some people believe conspiracy theories so adamantly and so profoundly, even against (and usually outright denying) all counter-evidence?

One of the main fundamental reasons is the psychological excitement one gets from the notion of being "in the loop", of knowing more than the average person, of knowing secrets that the majority of people are not privy to. Even if they don't consciously realize it, it gives them a sense of superiority: They know something that most other people don't, something that the majority of people are completely oblivious to. They have secret information, they know more, they are, in a sense, "superior" to the average person because of the privileged position of knowing the big secrets behind the scenes.

It essentially triggers a "superiority complex" of sorts in the brains of many people. It gives them a sense of excitement to know eg. governmental secrets that aren't open to the wider public. "I know something you don't." In fact, and perhaps somewhat ironically, even though they are trying to convince other people to believe the conspiracy theory, it just feeds this sense of excitement, this sense of superiority, when the majority of people don't believe them. It makes them feel superior to the "peasants" who have been brainwashed into believing the lies and can't understand the Real Truth behind the scenes.

Of course there's also the (somewhat childish) sense of satisfaction to "spill the beans", to tell other people the big secrets. It's a (rather childish) sense of "I know something you don't, want to hear what it is?" This is often associated with a smug attitude, and an attitude of pity if the other person doesn't believe it, which all feeds into the superiority complex.

If the other person believes it, then it gives a sense of satisfaction, a sense of being admired and adulated for knowing such things, for being so knowledgeable and so superior because of knowing the secrets. If the other person doesn't believe it, then it gives a sense of smugness and pity, a patronizing attitude, which strengthens the sense of superiority.

All of this is usually tied tightly to a strong aversion to admitting, even to oneself, having been wrong, having been fooled. This is usually why the cling so adamantly to the conspiracy theories they have been believing for a long time, even against the mountains of evidence against them: They consciously or subconsciously have an extremely strong aversion to being wrong, to admitting being wrong. They'd rather take the belief to their graves than ever saying to anybody, even to themselves, "I was wrong, I was mistaken, I was fooled." The more loudly and strongly they have been preaching the conspiracy theories, the stronger the aversion to recant.