The more one will try to accelerate an object, the more it will resist acceleration by raising it's total mass. Suppose there is an object somewhere in space that had never have any contact with Earth in the past. This object ALREADY have some vectorial speed relative to earth. Suppose this object has some kind of engine on board and fires it. If this action "adds" some speed to the object relative to Earth, the acceleration should be less than what it should be due to the object having more mass (as seen from Earth). It would imply that NOTHING in the whole universe moves faster than C, RELATIVE to ANY other things in the universe as if everything KNEW about the speed of everything else. How could this be ?