What do you get out of holding onto that thought? What’s the payoff? Why would you hold onto such a painful thought?
There may be many answers here that applies to a specific thought in a specific situation.
And there is also one I consistently find.
I get to blame someone else. I get to blame a person, circumstances, life, God.
And I get to avoid taking responsibility. I get to avoid seeing my role in it. I get to avoid seeing how I create my own pain and suffering. I get to avoid changing how I relate to life, and live my life.