**Core Concept**
The outcome of burns depends on the depth of tissue damage, primarily classified into three categories: first-degree, second-degree, and third-degree burns. The extent of tissue damage determines the severity of the burn and guides treatment decisions.

**Why the Correct Answer is Right**
The depth of tissue damage is the primary factor in determining the outcome of burns. First-degree burns involve only the epidermis, causing pain, redness, and swelling. Second-degree burns affect both the epidermis and dermis, leading to blistering and potentially scarring. Third-degree burns extend through the dermis and into deeper tissues, such as muscle and bone, resulting in significant tissue loss and potential organ failure. The depth of tissue damage is critical in determining the appropriate treatment, including wound care, grafting, and surgical interventions.

**Why Each Wrong Option is Incorrect**
* **Option A:** While the size of the burn is an important factor in determining the severity of the injury, it is not the primary factor in determining the outcome.
* **Option B:** The age of the patient is a significant factor in determining the severity of the burn and the risk of complications, but it is not the primary factor in determining the outcome.
* **Option C:** The presence of infection is a potential complication of burns, but it is not the primary factor in determining the outcome.

**Clinical Pearl / High-Yield Fact**
The Rule of Nines is a useful tool for estimating the size of a burn injury, with each body part assigned a percentage value based on its surface area (e.g., the head and neck are 9% of the total body surface area).

**Correct Answer:** D.