How many times have you had a fictional argument? Gone through multiple ways an interaction could go, varying in the amounts of realism involved in the scenario?

Sometimes this is good - introspection or using mental conversations or arguments can help you figure out how you feel about something, the pros and cons of a situation, etc.

The problem comes when it becomes repetitive. You spend time going over and over the same scenarios. Maybe you want to find other ways to handle them going forward. Maybe you’re frustrated by how you or someone else acted. Maybe you’re hoping for a future scenario where you’re correct and can ‘win’. Maybe this is how you’re punishing yourself for failing. This is rumination.