This document discusses the grammar structures "I wish I had..." and "I wish I hadn't..." to talk about regrets of things not done or things done that should not have been. It explains that "I wish I had..." is used to express regret over something in the past that was wanted to be done but was not. "I wish I hadn't..." expresses regret for something already done that should not have been. Examples are provided to illustrate the structures, and an exercise asks the reader to rewrite sentences using these expressions.