The first postulate of Einsteins special relativity theory says, that
“The laws of physics are the same for all observers in all inertial reference frames”
Which basically means, that if you’re in a train, travelling through a train station you can either assume, that you’re moving or not moving at all. A person standing on the train platform can assume, that he’s moving, and the train is standing still, or that his position is static and the train is moving (which would make more sense btw ;).
Well when I was a kid I always pretended the world is moving and the train is not. Einstein says thats a valid assumption but tell that to my parents. And why do I only have a C in physics? ;)