Certain kinds of feedback can also backfire. Even if the feedback is accurate, it can deteroirate performance.
Specific feedback that is aimed at process, method or technique is useful. If you liked a seminar, telling the speaker the parts of their session that resonated with you is good feedback. This feedback is actionable, and the speaker could choose to amplify those parts of the session.
Feedback that is aimed at a person’s ego can be harmful. Telling somebody that they are an outstanding teacher doesn’t help them improve their teaching, but is praise directed at their personality. This feedback isn’t actionable – knowing that they are a good teacher does not tell them how to improve their teaching.
The same applies to negative feedback. Criticism of process or technique can be harnessed by the receiver. Criticism directed at a person is often detrimental.
How do you know if a piece of feedback is good? Just ask yourself if the recipient can act upon it.