I've seen a previous threads where it was a mathematical consistency based on four-dimensions, and a host of other reasons. I'm currently trying to reconcile my belief that it has to do with time dilation and the observer effect.
I've read that. I am completely a layman in this rodeo. That math seems to be the only refuge for some. I was hoping that knowledgeable people here could possibly tell me if the observer effect had any bearing on two observable quantities, both being the speed of light.