Have you ever wondered how people can stand by and do nothing when something horrible happens right in front of them? Like with the recent allegations at Penn State, or when a toddler in China was hit by a car and nobody stopped to help. Surprisingly, experts say that inaction is more common than you think and there are several psychological reasons.

First, we think we’ll act more nobly than we actually do. For example, researchers asked if students would object if someone made a sexist remark in their presence and half of them said yes, but when someone made sexist remarks, only 16% of the volunteers actually objected.

Also, we tend to ignore the facts we don’t want to see. In one experiment, researchers tracked the eye movements of volunteers as they looked at pictures, some of which were X-rated. Those who felt uncomfortable, never looked toward the areas that they felt were inappropriate.

Another reason bystanders don’t step in: Normalcy Bias. Psychologists say that some people simply can’t process the horror in front of them. So, they simply shut down and pretend everything’s normal.

One final psychological reason people don’t intervene: The Bystander Effect. Researchers have found that the more people there are around to witness a crime, the less likely they are to intervene. Why? Because they figure somebody else will do it.