When people negotiate, the terms of the deal are affected by many factors. Imagine Greenland "cashes in" IOUs/goodwill to get better terms, only for the referen

When people negotiate, the terms of the deal are affected by many factors. Imagine Greenland "cashes in" IOUs/goodwill to get better terms, only for the referendum to fail. Then they change their mind a couple years later, maybe because an ally threatens them with invasion - they won't get the same deal again. Making requests to humans is never idempotent.