Teenagers, in particular, tend to think they are unique. They often feel alone. ”No one understands me.” They are biased to think that they are more unique than they really are. That’s because they have a small world view. Their world is their school and neighborhood, both of which were chosen by their guardian(s). They have not had sufficient time or opportunity to find people who are like them.
As you move from your teenage years into your 20s and 30s, you tend to have more opportunities to find new social networks. You meet new people at your university or job. You have choice in where to live. Over time you meet people who are like you.
We like people who make us feel good about ourselves. We naturally segregate to groups that share our values and have similar social status. For example, in nearly every neighborhood I have chosen to live, the people tend to be left-leaning, either non-believers or not overly religious and value science and education. Because I spend so much time with people who are like me, it would be easy to overestimate the percentage of atheists in the US population, for example. Often when I have a conversation with someone who is very religious, they tell me that I’m the only atheist they know. Like me, they have surrounded themselves with people like them. It’s the same way with politics. If most of our friends favor the same political candidate, we might overestimate that candidate’s popularity. There is the famous Pauline Kael quote: ”I don’t know anyone who voted for Nixon.” As a result of this in-group homogeneity, we no longer feel like as much of a minority.
There is another reason we are biased in the direction of underestimating our uniqueness. Our own mind is the only one we know. We only get to experience one lifetime. It is easy to fall into the trap of thinking other people’s minds are more like ours than they really are. For example, suppose you are unhappy. You might suspect that a lot of people who appear happy are really unhappy, but are just faking it. Alternatively, if you are genuinely happy, you might have less tolerance for someone who is unhappy. To you, happiness isn’t difficult to achieve, so why should it be for someone else? Or, suppose you are attracted about equally to men and women. You might suspect that most people are the same way, but pretend they’re not due to societal pressure. Alternatively, if you are strongly attracted to the opposite sex and never feel same-sex attraction, you might assume that people who claim to be bisexual are just trying to be trendy.
I think these are the two major causes of the false consensus effect.
The observant reader might have noticed something — that the opinions in this post might suffer from the same bias. I did feel isolated as an adolescent. I now have surrounded myself with people who are more like me than the general population. I only know my own mind. Maybe I am guilty of assuming that my story is more common than it really is.