His experience with both Rough and Oakes makes Rebus think out his prejudices and question how much a person is the product of his inherited nature, and how much nurture shapes that character.
Rebus considers his experiences with Rough and Oakes, prompting him to ponder whether one's character is primarily shaped by inherited traits or external factors. This reflection leads him to question how much of a person’s nature is predetermined and how much is molded by upbringing.