What he's basically saying (I assume at least) is that we build things based on past engineering efforts. There's that one story about how train tracks are the

What he's basically saying (I assume at least) is that we build things based on past engineering efforts. There's that one story about how train tracks are the size of a horse carriage during the roman empire era because of standardized size of roads at the time or something like that (too lazy to check it out). If you need to use vehicles like trucks and cranes to carry ISS boosters over a highway to their launchpad, you will be constrained by standardized sizes that, after all, come from the size of two horses side by side (that dictated the size of carriages and hence that of roads that carry people, etc).