Why do we feel déjà vu, and what causes it?

We feel déjà vu when our brain thinks it’s seeing something new, but it actually feels like something we’ve already experienced.

Imagine you're playing with your favorite toy car. You push it forward, and it zooms across the floor, that's what usually happens. But one day, you push it, and suddenly it goes flying off the table! It’s a little surprising, but then you think, “Wait… I’ve seen this before!” That’s déjà vu, like when your brain says, “Hey, I know this feeling!”

Your brain has two parts that help you remember things: one is fast and quick, and the other takes a little longer to work out what’s going on. Sometimes, the fast part thinks it already knows what’s happening, but the slower part hasn’t caught up yet, like when your brain says, “I know this!” before it actually remembers why.

This mix-up makes you feel like you’ve seen something before, even if you haven’t. It's like when you're halfway through a story and suddenly realize you've heard that sentence before, that’s déjà vu!