Continues…
“Achieving materially positive payload margin to a useful orbit with a fully & rapidly reusable rocket has eluded prior attempts. Many have tried to embark upon this path only to give up when it became clear that their design would have negative or negligible payload margin.
This is an extremely difficult problem to solve, given the strong gravity of Earth, whereas it is easy on Mars and trivial on the Moon. In the early years of SpaceX, I was not sure that success was even in the set of possible outcomes!
Fortunately, it just barely is, but requires doing unusual things like shifting the mass needed for final velocity attenuation and post-landing stabilization of the rocket (so it doesn’t tip over in wind) to the ground, rather than carrying heavy landing gear on both stages.”