For millennia, people have understood that they can cultivate themselves. At the most basic level, people can cultivate their physique through exercise, or their knowledge and skillsets through education. At a deeper level, people can cultivate their mind and character in ways that make them stronger in a more profound and essential way. In modern times, this idea of self-cultivation has largely been lost, but you do find reflections of the idea in some corners, including psychology, especially those areas of psychology that go beyond mental illness and look at cultivating mental wellness. That’s the realm of Steven Hayes’s new book, “A Liberated Mind: How to Pivot Toward What Matters.” The University of Nevada psychology professor penned the book before the pandemic hit. While it hasn’t taken off solely due to the pandemic, our society’s focus on mental health as a result of the prolonged crisis probably hasn’t hurt his sales. …