Jim has trouble deciding whether to buy a good-mileage, poor-maintenance mgb or a poor-mileage, easy-care camaro. Finally, he buys the mgb. According to cognitive dissonance theory, he will probably spend most of his time concentrating on:

the good mileage he gets

Explanation:

According to the cognitive dissonance theory, people tend to subconscious seek consistency when they are forming their personal decisions / opinion.

This also occurred when we choose a certain type of product.

Regardless of the brad, most customers tend to consistently choose a product with one or two distinct characteristics that they personally love. This is why Jim would concentrates most of this time on good millage when choosing his cars, regardless of the brand and other bad characteristic.