This is an excellent overview of the practical insights of cognitive science. And Simon adds a genuinely original contribution to the field: The idea that all our depressing thoughts spring from our universal tendency to compare ourselves or our circumstances to someone or something else. If the comparison is good, we feel good; if it is bad, we feel bad.
Of course, if you look at your own life in an overly negative or pessimistic way, your comparison may turn out worse than it really is, making you feel bad unnecessarily. And if you decide you're helpless to improve your state, that will make you depressed. From the simple idea of comparison, all the different modes of cognitive science are clarified and fit into the larger picture. Simon normally writes on economics. He wrote this book because of his own personal struggle with depression.