In this lesson from Bhagavad Gita for Your Daily Life by Ajay Tejwani, the author uses the the scene of Arjuna and Lord Krishna on the battlefield to illustrate the concept of happiness being the difference between reality and expectations. Arjuna's unhappiness stems from his expectation that he shouldn't fight his family, even though they are his enemies on the battlefield. This lesson is applicable to everyone's lives as we all face situations where our expectations clash with reality. The author urges readers to reflect on how they can apply this principle to their own lives, whether it be a teenager dealing with family conflict, a parent navigating difficult relationships, a professional facing workplace challenges, or an entrepreneur managing business expectations.