Here's why:

* Disease is a broad term: It encompasses anything that disrupts an organism's normal functioning. This includes infections caused by viruses, bacteria, fungi, and parasites, as well as genetic disorders, nutritional deficiencies, and environmental toxins.

* Evolutionary pressures: All organisms are constantly exposed to new and evolving threats. Even if an organism is resistant to one disease, it may be susceptible to another.

* Adaptation and change: Organisms can adapt to certain diseases, but this adaptation is never absolute. New strains of diseases can emerge, and organisms may evolve new weaknesses over time.

Even the most resilient organisms are affected by some form of disease. While some organisms might have more resistance than others, the idea of a completely disease-free organism is not realistic.