Feedback shouldn't include "but"
Don't you love when you are told "how great a job you did, but....."? The moment you add that but, you have most likely devalued the power of feedback and the person has now lost trust and possible interest. If you have created an environment of continuous feedback, you will never need to add, "but". This is an environment where positive or constructive (not negative) are given freely and equally received as a gift. It takes work to get there. Start by making sure that you generally give more positive feedback than constructive, over time.