If you're on a sufficiently smooth train and you close your eyes, you have no idea if you're standing at the platform or zooming across the countryside at 300km/h. That is precisely my point. Speed is perceived by the observer. Close your eyes and have nothing to perceive speed against. You need an observable marker to perceive speed. Open your eyes and you see the countryside going past at 300km/h. Acceleration is from a force (a=f/m) which you would perceive irrespective of whether your eye were open or closed. This is validation of Newton's three laws of motion.
