Everywhere you go, there's a quiet dark shape stuck to your feet. It copies your wave, your jump, your silliest dance. It never asks for a snack. So what is this loyal little tagalong, and why won't it leave you alone?

Here's the secret: your shadow isn't really a thing at all. It's a hole. Specifically, it's a hole in the light — a patch on the ground where the sunshine couldn't reach.

Light travels in straight lines, like millions of tiny arrows zooming from the sun. They fly and fly until they smack into something. And you, standing there, are a something.

Your body is not see-through. When those light arrows hit you, they stop. They can't sail through your shoulders and out the other side to land on the ground behind you.

So the ground behind you misses out. The light lands all around that spot, but not on it — you're standing in the way. That un-lit patch is your shadow, shaped exactly like you.

This is why your shadow can never wander off. It isn't chasing you — it's simply the place your body keeps blocking. Move your foot, and the missing light moves with it, because you took the block along.

Watch it change size, though. When the sun sits low at evening, the light comes in sideways, and your shadow stretches out long and skinny like taffy. High noon flattens it into a tiny puddle at your feet.

And your shadow isn't picky about who casts it. Trees do it. Buildings do it. Even the Earth does it — nighttime is really just our whole planet's giant shadow, cast into space as we spin away from the sun.

So your shadow follows you because you carry the very thing that makes it: your own solid self, forever standing in the sunlight's way. It's not spying. It's just proof that you're here, blocking a little slice of the day.