I love this lesson! I learned a long time ago the "why?" exercise. Things would upset me and I'd initially tag it with a reason: "they made me mad," or "they are so rude, disrespectful," etc. Or in a relationship, I would get angry because I perceived I was being treated unfairly. I learned that if I can take a step back and ask the all important question, "WHY is this upsetting me?" I would get a totally different response than what I initially thought. It often took several repetitions to dig deep enough to expose the real reasoning behind my emotion/reaction, but it was definitely not what I initially thought.
The lesson goes into further detail: "There are no small upsets. They are all equally disturbing to my peace of mind." Yet there are some "feelings" we hold onto because it is a form of self-definition. For example, anger. I know people that anger sustains them; it gives them drive and strength. Our popular culture is built on that--remember "Rambo" and "Dirty Harry?" All the main characters getting mad and then getting even.
I've often heard it said that whatever upsets you lives rent free in your mind. If you hold strong negative emotions, the only one being hurt is you. Don't pick and choose what to let go, live on the edge and release them all. Don't be afraid to fly...but first release the weight holding you down and back.