The document discusses regrets over past mistakes and missed opportunities. It provides examples of poor decisions people made, such as eating cookies for dinner instead of a healthy meal, spending too much money and not being able to pay bills, and turning down a good job opportunity. For each example, it suggests better decisions that could have been made, such as eating a healthy meal instead of cookies, saving money to pay bills, and accepting the job. The document also discusses using "should have" and "should not have" to express mistakes that were made and things that would have been a good idea to do but were not.