That statement relates to a feeling I have about burnout - I don't believe you fully recover from it. At least in my experience, while I (and others I've discussed this with) recovered by some point, I also felt something was left permanently weakened, in a way that made me increasingly susceptible to later bouts I'd experience.

There are probably normal factors that contribute to that, such as how much we age between bouts. However, after each bout, I recall not feeling the same after recovering as I did prior to when the bout started.