**Core Concept**
Lack of insight, also known as anosognosia, is a neurological symptom characterized by a patient's denial or lack of awareness of their own illness or disability. It is often seen in conditions such as Alzheimer's disease, schizophrenia, and stroke. This concept is crucial in psychiatric and neurological diagnosis.

**Why the Correct Answer is Right**
Lack of insight is indeed a feature of various psychiatric and neurological conditions. However, one condition where a lack of insight is not typically observed is in **factitious disorder**. Patients with factitious disorder, also known as Munchausen syndrome, fabricate or exaggerate their symptoms for attention and sympathy. They are often highly aware of their condition and may even be overly concerned about it.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because lack of insight is indeed a common feature in schizophrenia, where patients may deny their symptoms or refuse treatment.

**Option B:** This option is incorrect because lack of insight is also observed in Alzheimer's disease, where patients may not recognize their own cognitive decline or memory loss.

**Option C:** This option is incorrect because lack of insight can be seen in stroke patients, particularly those with frontal lobe damage, who may deny their deficits or refuse treatment.

**Clinical Pearl / High-Yield Fact**
A classic example of lack of insight is a patient with Alzheimer's disease who denies having any memory problems, despite being unable to recall their own name or address.

**Correct Answer:** D. Factitious disorder.