The title of the first chapter of both books is certainly the same: "Stop Feeling Sorry for Yourself." This is highlighted within the books, and elsewhere in interviews with Karl.
This is purposeful, designed to highlight one of the core issues holding us back. After that, the books are very different: one discusses happiness and our hidden journey toward it, the other talks about self-development and the quest to understand ourselves and the world around us. The writing style is simple and easy-to-understand, common sense and breezy. But there is also a certain depth to it that many reviewers here have picked up, and is obviously appreciated.
The book has been listed as free for a couple of days this month, so expect a few more interesting reviews.