Earlier quoted context omitted.
> What exactly did his companies deliver, that experts said was impossible, in the technological sense I mean? Landing the Falcon 9 booster on a droneship. As a physicist, I never believed it was impossible (the bar for “impossible” is rather high in physics) and yet an expert in the field told me it was!
I mean, people had demonstrated VTOL rocket landings before SpaceX came along. It was obviously just a matter of scaling it up and throwing tons of engineering man hours and test money at it, as SpaceX did.
The phrase "hindsight is 2020" applies to Elon's accomplishments in spades... anything he hasn't achieved yet is an "obvious con" and "impossible" while past achievements were "merely a matter of throwing engineers at the problem"...