I don't understand the author's claim that the sunk-cost fallacy has nothing to do with loss aversion because, "...[loss aversion] requires a comparison be mad

I don't understand the author's claim that the sunk-cost fallacy has nothing to do with loss aversion because, "...[loss aversion] requires a comparison be made between losses and gains." Any consideration of sunk costs is an implicit comparison against what might be gained by investing one's resources differently.