It's a beautiful teaching. Embodying it, practicing it, letting the habit of doing it become familiar (and almost delightful!) transforms us.
What does letting go on the practical level tell us? Letting go is different than denying or repressing. To let go of something is to admit it. You have to own it. Letting go is different than turning it against yourself; different than projecting it onto others. Letting go means that the denied, repressed, rejected parts of yourself, which are nonetheless true, are seen for what they are; but you refuse to turn them against yourself or against others. This is not denial or pretend, but actual transformation.
The religious word for this letting go is some form of forgiveness. You see the imperfect moment for what it is, and you hand it over to God. You refuse to let any negative storyline or self-serving agenda define your life. This is a very, very different way of living; it implies that you see your mistakes, your dark side, but you do not identify with either your superiority or your inferiority. Both are equally a problem.
Forgiveness is of one piece. Those who give it can also receive it. Those who receive it can pass forgiveness on. You are a conduit, and your only job is not to stop the flow. The art of letting go is really the secret of happiness and freedom.