If you mean crypto assets, take a look at my answer below.
Bullrun was happening in 2020-2021, while Covid19 was reported from China about 31 December 2019 for the first time.
So what does it mean? People who sold assets before Covid19 happened, cannot enjoy Bullrun. Is it the right decision? Surely not, man.
Well, I don't really understand the correlation between Covid19 and the timing to sell assets. We all know that no one knows when Covid19 will end. No guarantee to avoid Covid19 although you have got the vaccine. Also, no one can predict how far Covid19 can be mutated. From these matters, what we can learn and apply to our assets? I think what we can learn is only about "patient", not about "timing to sell".