Which of the following represents a symptom of delusions?

Erroneous beliefs are a hallmark symptom of delusions. Delusions are fixed, false beliefs that are not in accordance with reality, often remaining unchanged even when presented with contradictory evidence. These beliefs can vary widely, ranging from paranoid ideations to grandiose notions of personal abilities or identity. The persistence and conviction with which a person holds these beliefs is what distinguishes them as delusions rather than just simple misinterpretations or misunderstandings.

In the context of psychiatric symptoms, persistent feelings of sadness are more indicative of mood disorders, such as depression, rather than delusional thinking. Flat affect refers to the unresponsiveness or lack of emotional expression often associated with conditions such as schizophrenia, but it does not specifically relate to the beliefs that define delusions. Inability to perform daily activities can result from a variety of mental health challenges but does not specifically indicate the presence of delusions. Thus, erroneous beliefs are the definitive symptom that aligns with the definition and characteristics of delusions.