The fact that someone disputes an apparently self-evident or widely established claim does not prove that human knowledge is impossible. The existence of denial is not the same as the correctness of that denial. Misunderstanding, ambiguity, bias, or a specific objection can prompt rejection even of a secure conclusion.
Equally, calling a proposition “obvious” does not exempt it from identifying what grounds it. A careful discussion asks what precise proposition is disputed, what means of knowledge is offered, and whether the disagreement concerns evidence or interpretation.
This distinction prevents the existence of intellectual disagreement from being mistaken for proof that there is no reliable cognition at all.