It means that the speed of mutagenesis of a virus increases until it no longer poses a threat to the host due to molecular trade-offs. Considering molecular-orbital perspectives, it makes sense that the inclusion complex's overall energetic profile (nothing else is a virus, chemically speaking) remains constant. It means that mutations are in an internal competition. An advantage at the spike protein thus leads to a disadvantage elsewhere. Viral genetic trade-offs could be targeted for amplification.
This point is reached, for example, due to many transmissions and is accelerated by drugs, vaccinations, and the promotion of mild (or unfit) variants.
What we do to manage mutations?
It is a theory, and many have not yet clearly understood how it works.
References:
https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1008271
https://link.springer.com/chapter/10.1007%2F82_2015_463