Curiosity: “ZERO margin of error”?

The NASA Jet Propulsion Lab produced this music-thumping action video to explain the wondrously complicated plan for the new machine (which is called “Curiosity”) to enter the Martian atmosphere and make it safely to the planet’s surface. There is one teensy line of text, near the start, that is fun for starting arguments with any good engineer.

The video says that this complex design has “ZERO margin of error”.

Zero is, in its way, a big deal. Engineering, from one point of view, is all about building in as much margin for error as possible. Is this project the exception? Was it in fact designed to have…. ZERO margin of error”?