Einstein's 1905 light postulate says that the speed of light is independent of the speed of the emitter. This, combined with the principle of relativity, validly leads to the conclusion that the speed of light (relative to the observer) is independent of the speed of the observer as well. This conclusion has been tested countless times (Doppler effect, stationary source, moving observer) and the result is straightforward: the conclusion is false, that is, the speed of light (relative to the observer) does depend on the speed of the observer.
In order to detract the attention from this and other failures of special relativity, Einsteinians have devised the ultimate-cosmic-speed-limit red herring. "Nothing can move faster than light according to special relativity" is the mantra, although there seems to be no valid deduction of "nothing can move faster than light" from Einstein's 1905 two postulates. Needless to say, Einsteinians have also wasted billions and billions in experiments gloriously showing that "nothing can move faster than light".