And I've seen many rocks with different densities. Also making it a really bad idea to use as a reference.

Of course pre-metric units were defined by something convenient. A cubit is the length of the forearm.

I don't think Taleb goes into the why.

Metric is clearly superior if you have the social concept that units should be standardized and (as a corralary) that products are commoditized. The idea of a standard commodity, however, didn't really exist before the industrial revolution.

So why would units be standardized before that? The only place units mattered was taxes, and then the unit was whatever the king said it was.