Non-dual thinking is about embracing both ruggedness and flexibility in mindset. It is important for dealing with challenges in life. The concept of happiness is explored, with the idea that resistance to pain multiplies suffering. It is emphasized that striving for constant happiness can actually lead to unhappiness. Contentment is seen as a desirable state, as it allows one to appreciate both happiness and sadness without getting stuck on either extreme. The book promotes a mindset that can handle the inevitable changes in life and validates the concept of tragic optimism.