The 3M Rule for Stopping Rumination, from "Harvard University Open Course: Happiness" Lecture 7 "Adversity or Opportunity."

The first M is Magnify: exaggerate the facts that have already happened, such as overgeneralization or catastrophizing failure. If you didn't do well on a test today, think "I have no talent for studying, I will never do well on exams in the future." Clearly, it was just a mistake or lack of effort, but blaming it on a lack of talent only makes you more anxious and loses your motivation to move forward.
People with a "magnify" mindset tend to be perfectionists, expecting all A's or failure; failure is seen as a catastrophic disaster.
If someone doesn't reply, think "They definitely don't want to talk to me and find me annoying," or speculate about what you said wrong that upset them, feeling resentful and regretful inside. They probably are just busy and don't have time to reply.
Solution: Reflect on whether you are over-exaggerating the facts. Are you catastrophizing less important matters? Are your conclusions based on facts? Does not doing well on a test really mean you lack talent? There is no causal relationship at all. When questioning yourself, you usually realize you're exaggerating the negative effects and are jumping out of the disaster-thinking mindset.
The second M is Tunnel Vision: only focus on the failure part, ignoring the overall picture. Out of 50 students, 48 are focused and attentive, while 2 are daydreaming or dozing off. Think "The class is boring and the lecture is poor," focusing only on those 2 instead of the 48 who are paying attention.
Even if you study hard and perform well, being rejected from a job makes you feel incompetent; even if you look good, a breakup makes you think you're unattractive.
Solution: Consider whether you are suffering from tunnel vision, overly focusing on the negative parts. Question: Is the situation really that bad? Is my class really that terrible? Asking these questions helps you step out of emotional fog and face reality with rationality.
The third M is Fiction or Fabrication: making things up or personalizing blame onto others. If you dislike a subject in college and regret not switching majors, blaming your parents for choosing the wrong major. In fact, your major was chosen with your consent, and you had the opportunity to switch in your first year but missed it. Calm down and consider whether you're turning emotions into facts. Following the truth and reality can help you escape from overthinking.