Have you ever sat in a doctor’s office for hours, despite having an appointment?

Has a hotel turned down your reservation because it’s full?

Have you been bumped off a flight that you paid for?

These are all symptoms of overbooking, a practice where businesses sell or book more than their capacity.

So why do they do it?

Nina Klietsch explains the math behind this frustrating practice.

Lesson by Nina Klietsch, animation by Anton Trofimov.