He said:

If it doesn't have a URL, it doesn't exist.

This happened to be in a hallroom conversation at Digital Identity World, in the context of URL-based digital identity. But his insight is much broader.

The thought that immediately springs to my mind is Wag The Dog's "Of course it's true; I saw it on TV." It's that kind of profound.

Assume the internet keeps growing at the same rate for another decade or more. In some sense, it will be larger than meatspace. Assume innovations like tagging keep springing up in the future: tagging would have been impossible without all things worth tagging having URLs. URLs give those things a handle, a way of attaching to them. No URL, no way of attaching to them... and they disappear from sight.

If there's a thing changing in the forest and nobody can attach to it, does it make a sound, ahem I mean, does the thing really exist?

This argument has of course been the essence of why we came up with URL-based identity in the first place: people matter, so they should have URLs.