**Core Concept**
The distinction between neurosis and psychosis lies in the presence or absence of insight, which refers to the individual's awareness of their mental illness. This fundamental difference in cognitive perception is a critical aspect of psychiatric diagnosis and classification.

**Why the Correct Answer is Right**
Insight is a crucial parameter in distinguishing between neurotic and psychotic disorders. Individuals with neurotic disorders, such as anxiety or obsessive-compulsive disorder, typically possess intact insight, meaning they are aware of their condition and its impact on their lives. In contrast, individuals with psychotic disorders, like schizophrenia, often lack insight, failing to recognize their symptoms or the severity of their illness. This lack of insight is often attributed to the presence of delusions or hallucinations, which distort their perception of reality. The distinction between insight and lack thereof is a key factor in differentiating between neurosis and psychosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Severity is not the primary distinguishing factor between neurosis and psychosis. While some psychotic disorders, such as schizophrenia, can be severe, severity alone does not distinguish between the two categories.

**Option C:** Clinical features are an essential aspect of psychiatric diagnosis, but they are not the sole differentiator between neurosis and psychosis. Both categories can exhibit a range of clinical features, and the presence of specific symptoms does not necessarily determine the diagnosis.

**Option D:** Duration is not a reliable indicator of the distinction between neurosis and psychosis. Some neurotic disorders can be chronic, while some psychotic disorders may have an acute onset.

**Clinical Pearl / High-Yield Fact**
When evaluating patients with suspected psychiatric disorders, it is essential to assess their level of insight. A patient's ability to recognize their illness and its impact on their life can significantly influence treatment outcomes and overall prognosis.

**✓ Correct Answer: B. Insight**