What is an example of an irrational thought that can dominate someone's thinking?

An obsession is indeed a prime example of an irrational thought that can dominate someone's thinking. Obsessions are persistent, intrusive thoughts that cause significant anxiety or distress. Individuals experiencing obsessions often recognize these thoughts as excessive or irrational; however, the power of these thoughts can be so overwhelming that it becomes difficult to dismiss them. This can lead to intense preoccupation and mental preoccupation, affecting daily functioning and emotional well-being.

Delusions, while also irrational, are firmly held beliefs that are resistant to reasoning or contrary evidence, and they differ from obsessions in that they are often more fixed in nature and not recognized as irrational by the person. Rationalization involves justifying behaviors or thoughts with seemingly logical reasons, rather than addressing the actual underlying irrationalities. Compulsions are repetitive behaviors or mental acts that a person feels driven to perform in response to an obsession, but they aren't thoughts themselves. Each of the other options illustrates different psychological phenomena, but obsessions specifically highlight irrational thinking that intrudes upon and disrupts an individual’s cognition.