why does chief feel small and why does he see McMurphy as big?what is the irony here?who is the other character that chief refers to as big?

Physically, the Chief is a towering man. McMurphy is much smaller in stature. McMurphy, however, is charismatic and larger than life. MCMurphy commands attention while Chief, as big as he is, lurks in the shadows. He likes to be seldom heard of acknowledged.