With the measles outbreak bringing vaccination back into the spotlight, one question is rarely answered: Why do more people now choose not to vaccinate their children? In a word: Narcissism.

When the measles vaccine was introduced in 1963, American culture was very different. Children were not told they were special (at least not in a good way). The current mantras of “believe in yourself” and “just be yourself”—much less “I love me”—barely existed. College students were less likely to think they were superior to their peers than they are now. In short, individualism had yet to dominate American culture.

It does now, and individualism has crossed over into narcissism in many pockets of our culture. Narcissism is the perfect formula for choosing not to vaccinate your kids. No, not everyone who makes this choice is narcissistic, but the pervasive cultural narcissism in the U.S. makes these ideas possible and accepted even without individuals displaying the personality trait. Either way, it’s remarkable how many characteristics of narcissism map on to anti-vaccine ideas.

1. Narcissistic people believe they should be able to do what they want, no matter how it affects others. Parents sometimes state their belief that vaccines “are not the right choice for my child.” Because, apparently, their child is special, and should be able to opt out of something everyone else does. It’s the classic commons dilemma: We need everyone to do their part. If just a few people freeload, they can get the benefits without the risks. When too many people freeload, the system falls apart. That’s exactly what is happening right now with the measles outbreak.

2. Narcissistic people have less empathy. Those too young or medically vulnerable to be vaccinated are only protected if the vast majority of people get the vaccine, known as herd immunity. Because some parents exercise their “choice,” other people’s children can get sick or even die. But who cares, because I got to make a choice!

3. Narcissistic people have a hard time believing anyone knows better than they do. So unless they’ve done the vaccine testing themselves, why should they believe anyone who tells them vaccines are safe and effective? It doesn’t matter to them that study after study shows this and doctors and other authorities continuously say this.

Basically, the modern, narcissistic idea is not to trust anyone except yourself. In previous decades, Americans were more trusting, both of each other and of authorities such as doctors and the government. Recently, however, trust in others and in institutions have reached all-time lows. Apparently, Americans only trust themselves; everyone else is an idiot.

4. Narcissistic people are overconfident. In stock-market simulations, they take too many risks because they don’t expect to lose money. They’re special, so bad things won’t happen to them. Until they do—like children getting the measles because they weren’t vaccinated. This is also at the root of the argument that we should “let nature take its course,” that works until it’s you or your kid who gets sick and dies. But narcissism lets people believe it will never be them.

The science on vaccination is extremely clear: Vaccines save lives and are exceedingly safe. Characterizing the discussion around vaccines as a “debate” is misleading. It’s not a debate any more than evolution vs. creationism is a “debate.” There is no debate. Let’s move on to figuring out why people endanger their kids—and, more infuriatingly, ours—by not vaccinating their children.