Earlier quoted context omitted.
I think it's similar to the sub-5 minute mile in the sense that once something is shown as possible, others will achieve it as well.
It is also possible to land on the Moon, we know that. But no one else tried for more than 50 years. The barriers to becoming an agile space company are formidable. When looking at SpaceX, we forget how many space startups from that period are now defunct and forgotten. John Carmack founded one, too; it is gone.
An interesting fact is that they did very well as long as they could conduct cheap tests very often. As their rockets got bigger, they could no longer do that and then they floundered.