In this quote from James Patterson's "Private Vegas," the author suggests that certain individuals lack a moral compass, symbolized by a "big hole in their brains" where a conscience would typically reside. It implies that these people are devoid of guilt or ethical awareness, making them potentially dangerous or untrustworthy.
The statement highlights a stark contrast between those guided by conscience and those without it. It emphasizes how some individuals may behave selfishly or immorally because they are missing the internal voice that usually restrains harmful actions.