All Knowledge is Fallible

You can never have certain knowledge. That's the case even if you know it's coming from an infallible source. When he sits on the throne and speaks, it is said that the Pope will not err. Say this is true. Say that God himself channels down divine inspiration making this possible.

However, if you're watching him speak through a televised screen, there could be a glitch in the mic causing it to not register some parts, changing the meaning of the message; or perhaps a hacker installs a computer virus which scrambles the audio being transmitted, leading you to think he said something entirely different from what he did; or if you're hiding in the same room trying catch the voice in person, you may have been too far and misheard him; or perhaps he wasn't really sitting down properly in the way required to be infallible; or maybe it was a dress rehearsal and he was just acting out some fake dialogues he saw on TV the other day; or worse than all these, the whole affair which you bore witness to in person, in close range, after making sure he's sitting appropriately and doing the real thing, could have been a hallucination.

Any knowledge coming out of an infallible sources (of which none exist to be clear) can only be understood through methods and theories that are themselves fallible. There is no such thing as certain knowledge.