There are some thoughts that are negative and self-reinforcing, and it is useful to catch these and stop thinking about them. A few years ago I shared my thoughts and techniques with someone else and they found it valuable, so I am going to share it here.
My personal example was playing conversations in my head about or with a certain person. I would imagine them saying something and what my responses would be. The conversations would typically be of an argumentative nature. Sometimes the thoughts would arise from me doing something and wondering what the other person would think. I think it was my brain’s defense mechanisms trying to prepare me for conflict.
When I realize these kinds of conversations in my head, I try to see if they have value, and if not, to let them go. It is especially useful to realize when the “conversations” are unprompted, when I am not interacting or going to interact with the person. I’m not sure if the correct term is rumination, but that is the term that I internally use. Basically recurring thoughts or themes of thoughts.
A useful shortcut is saying: “Whenever I think about X, my head is not in the right shape and I need to get it better.” X could be an old job, a former relationship, or anything else that is not serving me to think about. Mere presence of X in my thought patterns is early warning that I am in a low or vulnerable state, and need to be vigilant.
There are times when it is valuable to think about undesirable past or future events. But it is best done with a clear head and an empty text editor, and then to be done with it unless some epiphany or major new event happens. In this way, I can get the benefits of learning from mistakes without continually revisiting them and wasting time and mental energy. There are some classes of thoughts that are wholly unproductive and feed on themselves, and so are best avoided. Awareness of them and their true nature weakens them and puts me back in control.