In "Shōgun" by James Clavell, a key lesson emphasizes the nature of thoughts and the effort required to cultivate a positive mindset. The quote suggests that negative thinking comes easily and unchecked can lead to a cycle of unhappiness. It highlights the human tendency to dwell on negative thoughts, which can spiral downwards if not consciously managed.

Conversely, the text underscores that fostering positive thoughts necessitates intentional effort and discipline. This "training" of the mind is an important concept, showcasing that maintaining a constructive outlook on life requires conscious action and practice, rather than allowing one's thoughts to drift aimlessly into negativity.