Prof. Robert Sapolsky teaches a class on Human Behavioral Biology. In his lecture on The Biology of Religion, he notes two traits that are often destructive and isolating in a secular context but quite adaptive in a religious context.
First, a “good” shaman is half-crazy — displaying what we now call a schizotypal personality, or, more simply, a quirky personality.
Second, a “holy” man in most orthodox religions excels at performing highly detailed, hours-long rituals, which revolve around cleanliness, food preparation, entering and leaving holy places, and numerology — that is, he’s obsessive-compulsive.
(Hat tip to Mike.)