Expanding on the classic work Thought and Choice in Chess, the author tests players from novice to master and describes how they approach complicated chess positions, then offers advice on how to avoid typical flaws in the thinking process at each level.
Great kick in the pants for this casual "Hope Chess" player to drop the shenanigans and play "Real Chess". I haven't read many chess books, but thought the de Groot exercises and documented protocols across the ratings spectrum were very insightful.
(Just realized there's an updated and expanded version...)