Maybe the word is defensive, not upset. If one becomes defensive that means they feel threatened. If they feel threatened perhaps they are afraid your going to prove what they know to be bullshit?

I have learned over a long and exciting life , to hold nothing as true . All anyone has are perceptions based upon their own personal experiences in life . We all know nothing at all, as all we think we know are just opinions. A closed mind struggles with the concept their belief could be challenged, as it means oh so much to them . The above theory made by Mr L Festinger seems flawed in itself . How many individuals of varying mentalities did he examine , or were these findings by way of studying people with psychological ailments ? We as a race are a diverse breed , we are not all in one group of mentality or fixated with one opinion, that we hold as true .Again this is just my own opinion on it all , we should stop wasting time psycho analysing everything so much. Personally i am a stubborn pig, as until i see with my own eyes i take very little as genuine, but then i hold very little as true anyway . Love and peace too you all.

Cognitive dissonance is in the mix, but it cuts both ways. As a believer, I had cognitive dissonance when experienced reality was never what my religious faith told me to expect. So I left the faith in large part to escape cognitive dissonance -- to have a more accurate mental model / expectation of reality.

The way I usually answer your question is that people over-identify with their beliefs -- they confuse their beliefs with the self. So questioning the beliefs becomes an existential threat, and they irrationally defend the belief in the mistaken notion that they're being personally attacked.

I have seen this both in and out of religion but it appears particularly rampant in religious fundamentalism.

Your phone is actually an evil gremlin that will eat your fingers.

Now try to believe that.

Goes against logic, common sense, empirical evidence. Reality. Everything you've seen and thought about your phone.

Even if it was a fucking Gremlin, you'd still have difficulty changing your mindset without proof, right?

Yeah, well. Faith requires no proof.

Your phone is a gremlin, and you must believe me CAUSE YOU'LL LOSE YOUR FINGERS OMG.

I'm so great for trying to protect you. I feel pride. I should share this with others. . So they too can protect people.

Etcetera.

TLDR is: Humans suck.

I once posted some meme on Facebook about some religious cognitive dissonance. I knew it was a bit controversial so I stated I just wanted to get people thinking about the conflict. A Christian friend commented, "But people don't want to think!" That made me laugh but it was an epiphany for me. She was right!

Because they believe they are right.

I actually disagree with this meme. While it is true that cognitive dissonance is what occurs when someone's beliefs runs counter to some information being presented, I actually think that the reason people sometimes get upset is because they often feel identified with whatever that belief is. If they weren't so attached to it, then they might not get so upset. In fact, someone could be right OR wrong about their beliefs, and not be upset upon being challenged, if they are emotionally intelligent enough.

Most humans most of the time prefer to associate with others who agree with them. It leads to less mental discomfort. While I experience this as well, I have, over the years, made it a habit to listen to all sides of a story reasonably, even if I cannot see a way that story can be accurate. The "upset" emotional reaction all has to do with emotional maturity or intelligence.

All that said, I can see the spirit behind the meme, and I understand what it is getting at, I just think it could be worded better. Thanks for posting!!

We all like to think that we've got it down. That our understanding of things is solid. It can be unsettling when our mental "floor" starts shaking with an earthquake of challenge . For many , a new idea is terrifying !