One core theme in 'Ikigai' is balancing extensive theoretical knowledge with practical application. The author emphasizes learning from multiple disciplines and applying that knowledge to solve real-world problems. For instance, the protagonist studies social sciences, economics, and governance and approaches strategy with a rational mindset. This disciplined learning and application method is captured in the quote, 'I study social sciences, economics, governance. I am a strategist. I am trying to turn off emotions and sentiment and be rational when I study strategy.'