You might have heard this theory before on the Internet: It’s the idea that, in a group of 23 people, there’s a 50 percent chance that two of them will share the same birthday. This means that the guy in front of you at Starbucks—who also ordered the pumpkin spice latte with two pumps of toffee nut syrup—might be your birthday doppelgänger. The world is truly small. Crazy, huh?

But let’s be real—this is one of those factoids floating around the internet that sounds like complete bullshit. But is this theory actually true?

“This [hypothesis] is absolutely correct,” says Ray Goerke (otherwise known as Reddit user Sirkuss) in a recent post in the Ask Science community.

According to Goerke, a Ph.D. student in physics at the University of Toronto, this hypothesis is called the Birthday Paradox, because it’s a “well-known counterintuitive result.”

Here’s why it just seems so improbable: There’s 365 days in a year. If you pick a random person, there’s only a 1/365 chance that you share the same birthday. That’s pretty damn small. So how can this be true?

Turns out, we’re rationalizing it the wrong way. The odds are low if you compare yourself to a single person. There are 22 other people in the other room with you.

Masoud Shakiba via PLOS One

“There’s a total of 253 possible pairs and any of them have a chance of having the same birthday,” explains Goerke. That’s a lot of different pairs. When you do the math, the probability that nobody shares the same birthday out of all those pairs is around 50 percent.

And as Reddit user kreggLUMPKIN pointed out:

“As is the case with George Costanza, your intuition is almost certainly wrong and the correct solution is the exact opposite of what you [imagined].”

Birthday cake gif: jeweledqueen/Tumblr