Re: I don't get it ...
There are two issues that are counter-intuitive. Firstly, how we all add velocities in a normal common-sense way is wrong. It is nearly enough right if you are dealing with slow things like cars or bricks but it is in fact incorrect, and the proper way to add or subtract relative speeds can be derived in a straightforward way, see Lorentz instead of Galilean transformation.
Second, the maximum speed limit (that the first point relies on as an assumption) actually falls out of the nature of spacetime - it is a fundamental parameter of our universe, in the same way as the strength of gravity or the value of the charge on an electron is.
So, sadly, you can't just strap more rockets on and keep getting faster til you break the limit.