[baud147258]

> Often A isn’t useful without B, and B isn’t useful without A. For instance, A is chariots and B is roads.

Even without chariots, road are useful: pack animals and people on foot will move much more easily if there is a solid path that doesn't turn to mud when it's raining, that's clear of obstacles and relatively smooth.

[dragonwriter]

> Even without chariots, road are useful

And vice-versa; chariots are, after all, implements of war that fight off-road.

While A requires B and B requires A may exist elsewhere, chariots/roads is a particularly poorly chosen example.

[wickawic]

It was a contrived example but charitably there are lots of inventions that are only useful in light of other inventions.

[baud147258]

Yes, I was just criticizing the example chosen, not the explanation itself (and judging from the votes, I was unclear).