[pdonis]

> The coincidence of wants is likely a myth.

Humans operate by doing each other favours.

But intuitive tracking of who owes you favors and who you owe favors to does not scale. The double coincidence of wants problem is not a myth; it just doesn't come into play until you start dealing economically with groups that are too large for intuitive tracking of favors to work--roughly, groups larger than the typical hunter-gatherer tribe.

[kragen]

As we see in the comments above, the gift economy scaled to include Bronze-Age Mesopotamian international trade. It's true that a Hittite in Hatti wouldn't know everyone in Nineveh, or indeed anyone, but he knew the Hittite king, who knew the king in Nineveh.

[jotakami]

Or if you doubt that you will ever meet that trading partner again, or if you just don’t trust them and there is no legal framework for recourse if they screw you over...