Cotard's syndrome is characterized by what belief?

Cotard's syndrome is a rare neuropsychiatric condition where individuals harbor the belief that they are dead, do not exist, or have lost their internal organs or blood. This belief often extends to feelings of nihilism, where the affected person may think that the world around them or even their own existence is an illusion. The hallmark characteristic of Cotard's syndrome is this profound conviction of nonexistence, which distinguishes it from other psychiatric conditions.

The other options present beliefs associated with different psychological phenomena. For instance, the idea of being a famous celebrity relates more closely to delusions of grandeur, commonly seen in conditions such as bipolar disorder or certain types of psychosis. The belief in one's non-reality aligns with depersonalization or derealization syndromes rather than Cotard's syndrome specifically. Lastly, the notion of invincibility is often associated with manic episodes or certain psychotic disorders. Thus, the defining feature of Cotard's syndrome is indeed the belief that one is dead or does not exist, making that the correct answer.