The first time Finn had to kill someone, he was messed for days. He knew that person had a family, and that they just doing what they had to do to protect them. That’s why Finn takes the aggression during a mission, so that Holley never has to go through what he did.
Mater mentioned that he fell in love with a pinkish purple, British, sophisticated, jaguar/pick up truck hybrid named Doreen in Cars. Strangely, Holley Shiftwell fits that description to a T. Because Holley is a sophisticated, British, good-lookin’ jaguar. Maybe, just maybe Holley IS in fact REALLY Doreen, but she was on a spy disguise test mission disguised as a TRUCK/jaguar hybrid in Radiator Springs back then.