“Who ever said knowledge is complete? It certainly wasn’t a scientist.”
Scientists probably don’t say it, they just operate like that — “my professor said it, I believe it, that settles it.”
Most prominent scientists have reputations to protect.
They certainly don’t want some genius grad student proving that the “expert” got it all wrong when “the expert” won that Nobel prize.
That is why there is the saying:
“The best way for science to advance is for the old scientists to die.”