As if massive exponential growth is not bad enough, some viruses like HIV, influenza and COVID19 are just getting started. They have another physical property that will cause them to evolve for maximum efficiency for what they do best: replicating themselves. They will change and evolve. Viruses do this by changing their own program, their own RNA sequence in the case of COVID19, and they do it frequently.
One of the first virus proteins made by our cells from COVID19's RNA template is an RNA-polymerase, which takes care of making copies of the virus RNA program itself. The problem with this, from our point of view, is that viral RNA-polymerases have low fidelity. They make lots of copy mistakes about every 1/10,000 RNA-bases. COVID19
So while community leaders and politicians wish for the best-case scenario as they partially follow the recommendations of public health scientists, the thousands of mutations changing COVID19 RNA every week in just a single person has the potential to keep this pandemic going for a long long time.
The only way to stop it is to prevent the virus from infecting the next person and so on. That is best done with vaccination and masking up, but we are failing to clamp that lid on tight at this point in time and that is why we are now gambling with the variants of COVID19.