Is that most of the time, what you're seeing probably isn't one. While Matthew Inman's descriptions (including visual) of why one might feel uncomfortable around new-to-them facts rings true and sounds rather like a fact, a new study suggests the backfire effect may be "a very rare phenomenon" that's not impossible to overcome.
People entrench around factually wrong information for many reasons: personal or in-group bias, feeling an emotional or intellectual discordance, thinking their view of life or actual way of life is under threat, rhetorical or semantical differences, philosophical disagreements...whatever. Calling it a backfire effect - and explaining it by what goes on in your amygdala - does little justice to what disbelieving a fact actually involves. It has little to do with brain chemistry, which I'd say is more a part of the process of fact-disbelieving than its direct cause.
Let me change your mind: people can be convinced to change their minds through a process called "factual intervention".
Which reminds me: people can convince themselves they hate something. Anything. Matthew's image of a house with walls scrawled over with formative reasons for disbelieving facts, which bizarrely enough includes the phrase "hatred of cilantro"? Cilantro is probably on there because it's not something you hate - there are several genes that actually change the flavor of it for some of us. Judging by how I think
soap cilantro tastes, I also have the little buggers.
While I'm on the topic of not accepting facts, and while I'm still on the topic of science in general (yes, starting this paragraph counts), science is never a settled question. Some of the latest food studies seem out to prove it by pronouncing butter bad for us again and salt better for us than we thought. It can even help people lose weight, but in doing so increases loss of both fat and muscle, so I'd take this news with a pretty large grain of, uh...