Turning a problem over repeatedly feels like working on it. Research on rumination consistently finds the opposite, that the more time is spent in this mode the worse both mood and actual problem solving become.
It borrows the form of analysis
Rumination involves attention, effort and a sense of engagement with something important. All of the surface features of thinking a problem through are present.
What is missing is the output. Analysis narrows towards a decision or an action; rumination circles the same material without converging on anything.
Because the effort is real, stopping feels like giving up on the problem rather than abandoning an unproductive process.
The questions asked are unanswerable
Productive reflection tends to ask what can be done, which has answers. Rumination tends to ask why something happened or why a person is the way they are.
These abstract questions have no terminating condition. Each attempted answer generates further material of the same type, which is what produces the loop.
Studies that prompt people to shift from abstract to concrete questioning about the same event find that mood and problem solving both improve.
It is intermittently reinforced
Occasionally the process does deliver something useful, an insight or a decision. Behaviour that pays off unpredictably is unusually persistent.
The rare payoff is enough to sustain the pattern through many unproductive episodes, in the same way that occasional wins sustain other repetitive behaviours.
This makes rumination resistant to the observation that it is not working, since the person can recall occasions when it did.
Attention narrows onto matching material
Sustained focus on negative content changes what the memory system retrieves. Related material becomes more accessible and unrelated material less so.
The result is a self-confirming sample. The evidence appearing in mind seems to support the conclusion, because the retrieval process was already biased towards it.
This is the mechanism behind the observation that rumination reliably lengthens episodes of low mood rather than resolving them.
Why interruption works better than argument
Attempting to reason with ruminative content feeds it more material, because the reasoning becomes part of the loop.
Approaches with evidence behind them tend to target the process instead, through shifting attention to concrete external tasks or scheduling a bounded period for the concern.
Where rumination is persistent and tied to low mood or anxiety, it is a recognised treatment target, and assessment by a clinician is the appropriate route.