"You got to understand that as soon as a man goes to help somebody, he leaves himself wide open. He has to be cagey, Billy, you should know that as well as anyone..." (p. 121)
I think that what Chief Bromden meant by this is basically if someone needs help, help them but, don't forget about yourself in the process. He also might be telling Billy to be "cagey" because of his stuttering, people might thinks hes more crazy than he really is.
We read Chief Bromden's view of the ward and hows theres this fog machine, and how it hides everything behind it and when the fog finally lets up everything is ten times clearer. And how he can barely hear Billy Bibbit and some other people talking about Billy's stutter, but he can't see them behind the fog. The fog is not literally a fog, but a metafor for how the patients in the ward don't see whats really going on there, and because McMurphy is letting some of the patients know about what is really going on in the ward he is "clearing the fog" for them.
Chief Bromden also finally understands what Billy has been talking about for the six years he has been in the ward. Billy is talking about how America is like a flag, a watermelon and a peach. And how Mexico is like a walnut, acorn and that its wooden.
