Short excerpt from a YouTube talk by Eckhart Tolle explaining that grievances nourish and empower the ego; a surviving grievance indicates the ego is still operating and can persist even while other aspects of awakening progress.
The ego derives sustenance from the grievance and strength from the grievance. So if you harbor a grievance, that means that the egoic self is still operating. It is not you who is harboring the grievance. It's the ego in you that is harboring the grievance. So if you have a surviving grievance in you towards another person, you need to know that ultimately it's not you, it's the ego. It's still operating. So you can develop in other areas of your life, and the ego can remain in you, even can attach itself. Let's see. You're awakening beautifully. But there's one corner in your mind where the ego survives because it has attached itself to a grievance.