In COVID-19's case, there's a reasonable chance that it's a synthetic product of gain of function research.
https://www.newsweek.com/dr-fauci-backed-controversial-wuhan...
There's evidence that it's synthetic
https://yurideigin.medium.com/lab-made-cov2-genealogy-throug...
https://nerdhaspower.weebly.com/ratg13-is-fake.html
Most of the researchers who are strongly denying the possibility of COVID-19 being synthesized in a lab have conflicting interests. Namely, they are associated with organizations that have directly collaborated with the Wuhan Institute of virology.