Thinking starts in the orbitofrontal cortex and here problems and mistakes are identified.
When a problem/mistake is detected the orbitofrontal cortex signals the cingulate gyrus of an issue.
The cingulate gyrus initiates stress and anxiety.
Working with the cingulate gyrus is the caudate nucleus, which is responsible for changing thoughts from one to the next.
If the brain identifies a problem it's normal for the caudate to be inefficient and allow a loop to occur. The caudate can get stuck in a problem.
If you break the problem into smaller steps this helps the caudate to get un-stuck.