"On the list of leadership merit badges, “Successfully deliver hard news” is one the hardest badges to acquire." -- Michael Lopp with a short and important post on how to deliver hard news or feedback. The first couple of tips on writing your feedback down and sharing it with a neutral person is something I saw (sadly) too few people do. You need to understand and answer these questions, and it's extremely hard to do it well without serious preparations: "What do you want the other person to take from it?", "Is it the most constructive way to phrase it?", "How would success look like if they will act now?", "Is there some time constraint that you think is important for them to know?".