A coincidence is when two or more things happen at the same time or in the same way purely by chance, with no planning or connection between them. When you randomly think about your friend just seconds before they call you on the phone, that's a coincidence. When you and your classmate both wear the exact same shirt to school without planning it, that's a coincidence too.

Coincidences feel surprising or even a bit magical because our brains naturally look for patterns and connections. When you run into your neighbor at a restaurant fifty miles from home, it seems remarkable because what are the odds? But mathematicians point out that with billions of people doing millions of things every day, unlikely things actually happen all the time.

Sometimes people say “that's quite a coincidence!” with a skeptical tone, suggesting they think there might actually be a hidden connection or plan. Other times, coincidences are just amusing surprises that make life interesting. If you discover that your new friend shares your birthday, loves the same books, and has a dog with the same name as yours, you might wonder if it's pure coincidence or if you're meant to be friends. Either way, coincidences remind us that the world is full of unexpected connections.