Final answer:
Persistent irrational fear and distrust of others is the symptom that is commonly associated with both Paranoia and Schizophrenia, as it aligns with the delusional aspects of schizophrenia and is a hallmark of paranoia.
Step-by-step explanation:
The symptom or behavior that is commonly associated with both Paranoia and Schizophrenia is Persistent irrational fear and distrust of others.
This is because both paranoia, as a symptom, and schizophrenia as a mental disorder, often involve intense anxious or fearful feelings and thoughts that are not based in reality. In the context of schizophrenia specifically, a subset of symptoms known as 'positive symptoms' includes delusions and hallucinations, which can manifest as paranoia. The irrational distrustful and fearful thoughts can be a significant part of the delusional aspect of schizophrenia, often leading to a distorted view of reality where the individual believes that others are out to harm them without reasonable evidence.
Other symptoms of schizophrenia, such as hallucinations, delusions, and disorganized thinking can contribute to a person's paranoid thoughts and behaviors, reinforcing the fear and distrust of others.