by Jenna C, ’26

Dear Jenna,

I was at a movie the other night, and right when it got to an important scene, the person next to me kept checking their phone. The screen lighting up was already distracting, but then their phone started buzzing and even rang once. It completely took me out of the moment, and I could tell other people around us were getting annoyed too. The person on their phone probably didn’t think it was a big deal, but it affected everyone trying to watch the movie.  Why does one person‘s behavior end up impacting everyone else like that?

From,
Distracted in the Dark

Dear Distracted in the Dark,

What you are describing is a really clear example of something in economics called an externality and once you start thinking about it, it shows up in way more situations than you would expect.

An externality happens when one person‘s actions create a cost or benefit for someone else who is not directly involved in the decision. In your case the person checking their phone gets the benefit of doing what they want at the moment, but the cost gets pushed onto the rest of the audience. You and everyone around you become that third-party, even though you had no control over the situation.

What makes this concept more interesting is that externalities can go both ways. They can be negative, like your example, where the experience of watching the movie is disrupted, but they can also be positive. For example, when someone is fully engaged and respectful in a shared space, it helps maintain the experience for everyone else. It’s the same idea just with a different outcome.

Once you start viewing situations through this lens, it is hard to unsee. It becomes clear that most decisions are not just individual, they have spillover effects. Your example is a small one, but it reflects a much bigger idea that shows up in everything from shared spaces like theaters to traffic to environmental issues.

Best of luck!
Jenna 

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