(n.) The tendency to overestimate what a compromise actually bought you, because the cost of the compromise is felt directly while its benefit has to be inferred. In short: the size of what you gave up becomes the estimate of what you gained.
Sibling to the sunk cost fallacy, not its logical opposite. Both price an option by the pain attached to it rather than by what it actually returns — sunk cost looks backward at what was already spent, forgone cost looks sideways at what was declined.