Quote: Like running inside a box car in a moving train. You run 10mph relative to the box car, but relative to the ground you're doing You+Train.
Now assume that the train is travelling at the speed of light.
...through a dark tunnel...and then it turns on its headlights! Can you see anything? What if you point a flashlight backwards down the path you've taken at lightspeed- are those photons 'moving' at zero velocity?