**Core Concept**
Koebner's phenomenon refers to the appearance of skin lesions on previously unaffected areas of the skin following trauma, including minor cuts, scratches, or burns. This phenomenon is observed in various dermatological conditions, including psoriasis, vitiligo, and lichen planus.

**Why the Correct Answer is Right**
Koebner's phenomenon is a result of the body's abnormal response to skin injury, leading to the development of new lesions. In psoriasis, for example, the trauma triggers an abnormal immune response, causing the activation of keratinocytes and the release of pro-inflammatory cytokines, resulting in the formation of new psoriatic plaques. This phenomenon is thought to be mediated by the expression of certain adhesion molecules and the activation of various signaling pathways.

**Why Each Wrong Option is Incorrect**
**Option A:** Psoriasis is a classic example of Koebner's phenomenon, where skin lesions appear on previously unaffected areas following trauma. Thus, this option is incorrect.

**Option B:** Lichen planus is another condition that exhibits Koebner's phenomenon, where skin lesions appear on previously unaffected areas following trauma. Therefore, this option is also incorrect.

**Option C:** Vitiligo is a condition characterized by the loss of skin pigment, and it also exhibits Koebner's phenomenon, where new lesions appear on previously unaffected areas following trauma. Hence, this option is incorrect.

**Option D:** This option is correct because it is the exception. The correct answer is not listed.

**Clinical Pearl / High-Yield Fact**
Koebner's phenomenon is a useful clinical clue to diagnose conditions that exhibit this phenomenon, such as psoriasis, lichen planus, and vitiligo. When a patient presents with skin lesions on previously unaffected areas following trauma, it is essential to consider these conditions in the differential diagnosis.

**Correct Answer:** D.