I’ve come here expecting to discuss the matter too!

I tried to explain myself using the marginal nature of value:

– we need to drink a few liters of water a day, so it’s likely that an ounce of water comes at a time and place where we already had some – and if we are thirsty, we make sure to have some readily available. In the desert (beautiful in Dune from Herbert) water is a matter of life and death because of its scarcity, so we are close to the “zero”, or maximum marginal value, and people might be ready to kill for some of it

– diamonds on the other hand are very scarce and hard to make, so it’s very likely that an ounce of it is “zero” in almost every free trade it’s subject to, which means maximum marginal value almost all the time. Therefore it’s very likely that an ounce of diamonds is not held readily available by most humans. To disprove my point, no human would prefer to hold diamonds while dying of dehydration at an oasis, so there are exceptions as well.

– the conclusion is around price(or cost) and value, but I’ll stop here to keep the thread without spoilers