The quote from Richard Bachman's book "Rage" suggests that a person's character is vital in determining their capability and reliability. If an intelligent person possesses a flawed character, those flaws become evident in their actions and decisions. This highlights the importance of integrity and ethics in individuals who are intellectually adept.
On the other hand, if they have a strong character, their intellectual abilities become predictable and dependable. The comparison to calculating square roots emphasizes that when someone's character is sound, their reasoning and decisions are straightforward and clear, making it easy to understand their thought processes.