Very well written! Co-habit or co-existence is important, as you have said. Ecosystems are the very prime examples. Even Covid-19 is highly adaptable to humans because it does not kill its host often. A dead host is a dead end for viruses after all. But its high adaptability may backfire us as more cases = more deaths, which is partly also driven by poor immune health.

Its partly because young or old people without any comorbidity may still succumb to Covid-19. In such cases, high viral load entering the respiratory tract, genetic factors, or age-related stiffening of fibroblasts may have played a role. But knowing there are factors we can't control, preserving our own health proved to be even more important.