What does Mack learn at the pool

When the patients make their weekly trip to the pool, McMurphy learns that she really does have insurmountable power over them. The realization comes in a single moment, when McMurphy discusses with a lifeguard how the hospital is better than a jail. The lifeguard points out to him that, at least in jail, a person has a definite release date. The lifeguard, who is also a patient, tells McMurphy that he was picked up for drunkenness and disorderly conduct and has now been in the institution for nearly nine years. McMurphy will be there as long as Nurse Ratched intends to keep him.

Later in the story, we see the pool become a symbol of rebirth when McMurphy joins the men and seems to dunk them in baptism. References such as this depict McMurphy as a savior.