Definition
Someone who loves mint chocolate chip might say, "Of course more than half of everyone likes it!" That's the false consensus effect: a psychological tendency to think your own opinions and tastes are far more common than they really are. You assume other people feel and judge things the way you do, so you treat your own view as plain common sense.
Why do we assume everyone else thinks like us?
When you pick lunch, have you ever thought, "On a day like this, it's obviously hot gukbap (Korean rice soup)!" and assumed everyone around you wanted the same thing?
We mostly spend time with people who share our tastes and values. When we keep running into reactions similar to our own, our views start to feel like the average for the whole world.
Psychologist Lee Ross's famous sandwich-board experiment shows this well. In a 1977 study, students were asked if they would walk around wearing a silly advertising sign. Students who agreed guessed that about 62% of other students would agree too. Students who refused guessed that about 67% would refuse.
Both groups firmly believed that their own choice was the ordinary choice of the majority. We tend to overlook people who think the opposite of us. Instead, we take the experience that pops into our head first and treat it as a picture of the whole world.
Social media and algorithms can make the illusion stronger
Turn on your phone, and your feed fills nonstop with videos and news from topics you care about. When you see comments and likes from people who think like you every day, it's easy to feel sure: "I knew I was right. The whole world agrees!"
This kind of personalized algorithm can lock the illusion in even harder, because voices that disagree with you show up less on your screen. Research is mixed on how much algorithms actually narrow what people think, and there are several views. But it's clear that it's easy to stay in a small room and mistake it for the real public opinion of the whole world.
This illusion also causes conflict in conversations. If you believe your view is plain common sense, then when you meet a different opinion, it's easy to blame the other person and misread them: "Why are they so unreasonable?"
A little more precisely
The false consensus effect doesn't mean insisting that your group is always the majority. The key is a mindset in which you overestimate the share of people who agree with you, compared with the real statistical share. Even if you know yours is a minority view, you still think, "Still, more people must be with me than you'd expect," and inflate the number.
Another interesting point is that it should be told apart from its opposite, "pluralistic ignorance." Pluralistic ignorance is when everyone feels uneasy inside, but stays quiet because they think, "Everyone else seems fine with it." The false consensus effect, by contrast, is when you think, "Others must think like me," and lay your own standard over them.
The first step out of this illusion is very simple. When the words "Doesn't everyone think so?" are about to leave your mouth, you need to quietly remind yourself that the world you know is not the whole world.
Common misconceptions
The false consensus effect only shows up in people who are strongly opinionated and stubborn.
It's a universal cognitive bias that anyone can experience, whatever their personality. That's because everyone judges the world by first recalling their own experiences and memories.
Where you meet it
When your favorite idol group makes a comeback, you assume everyone in the world is listening to that song.
You walk out of a hard exam and jump to the conclusion, "Everybody must have gotten that question wrong."
In one sentence
It's a mental illusion in which you assume others share your thoughts and tastes, and so you believe your opinion is more widespread than it really is.