One of the biggest surprises in our understanding of Physics came in 1905 with Einstein's paper on Special Relativity.
The most striking property of Newton's laws of mechanics is that the laws are the same in any coordinate system moving at a constant velocity. Einstein extended the symmetry that the laws of physics are the same in any inertial coordinate system to Electricity and Magnetism which had predicted the speed of light.
The Einstein principle of relativity states that ``All of the laws of Physics are the same for every inertial observer''. In particular, ``The speed of light is the SAME for all inertial observers, regardless of the motion of the source''. But this required some big changes in our basic understanding of time.