This book is amazing. It provides concrete examples based on a wonderful study of a group of Harvard graduates of how different psychological coping methods helped people succeed or fail during their lives.
Its most important finding, in my view, is that peoples circumstances in life play no role in their eventual success or failure. Instead, it is the coping methods that people develop, and the positive effort they put in, that decide their outcomes and happiness.
Most chapters contrast 2 real people from the Harvard study, identifying the opposing psychological methods each used (i.e. one is a procrastinator and another gets things done) and shows how their lives played out. Their behaviors correlated directly with their happiness and success in life. The procrastinator wandered from one job to the next, did not have satisfactory relationships, and did not build wealth. The person who got things done succeeded in business and in personal life.
This book identifies the key mental characteristics necessary to adapt to life, using concrete examples based on a long-term study. It provides a positive message that the circumstances of these subjects birth and background did not matter nearly as much as how much effort they put into life. It is well worth reading.
On the other hand, it is worth noting that these graduates were predominantly white, at least middle-class, often Protestant, and were part of the "greatest generation" that as WWII veterans worked during a time when the US economy was booming.