Final answer:
Emotional stability is not a component of physical fitness, as it refers to the psychological aspect of well-being, unlike body composition, muscle strength, and cardiovascular endurance, which are related to the physical body.
Step-by-step explanation:
The core component of well-being that does NOT belong with physical fitness among the options provided is D. Emotional stability. Physical fitness is generally characterized by attributes such as body composition, muscle strength, and cardiovascular endurance, which are directly related to the physical condition of the body and how well it performs physically demanding tasks. Emotional stability, on the other hand, pertains to the psychological aspect of well-being, which involves the ability to manage emotions and maintain psychological health even when faced with stressors. This distinction makes emotional stability an outlier when discussing physical fitness components.