Distinction bias, a concept found in decision theory, is the human tendency to view two options as being more distinctive while being compared to each other than if they were being evaluated separately.
For instance, someone is trying to buy a house. They may have reached a point where they are trying to decide between two similar houses and are comparing some details such as a master bathroom with a sunken tub as opposed to one with a walk-in shower stall. While these two details would seem trivial early in a house search, they could make or break a later stage of the purchase decision.