User talk:2A02:8071:B180:7D00:FCF7:DD1:EFD:DAD8

I can't understand this sentence in quotes from the intro:

(He used the black swan fallacy to discuss falsification.) "If the outcome of an experiment contradicts the theory, one should refrain from ad hoc maneuvres that evade the contradiction merely by making it less falsifiable."

what does "making it less falsifiable" mean? In the black swan fallacy, does it mean that a person should not just add the additional premises of "..all swans are white, except the black one" or what is an ad-hoc maneuver?