By Ainissa Ramirez and Salima Koroma
September 18, 2015

The coin flip is so synonymous with randomness that the phrase has become a metaphor for unpredictability itself. We even trust the coin toss with our nation’s most popular sport: Every NFL game begins with a flip to decide which team will kick or receive.

But while everyone intuitively knows there’s a roughly 50-50 chance the coin will land on either side, few understand exactly what makes a coin toss random in the first place.

Watch the video to find out the answer.

Contact us at editors@time.com.

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