In Part 3 of the novel, How does McMurphy build up the men's confidence at the gas station?

He uses "logic" to try to convince the men at the gas station that these "insane" guys should be treated very well because they could hurt the gas station attendants. He suggests that with someone like the Chief in the group (he is so huge), the attendants had better be careful. The men "buy into" the idea that they have some power based on their perceived (and in some cases legitimate) insanity. While it is not real power, McMurphy's way of handling the gas station attendants helps the men feel more confident.