The only absolutely sure way of determining any truth is by direct experience and observation, since any supposedly authoritative source, no matter who or what it is or was, no matter when it came into being, may be compromised in some way.

If people are brought up to believe that the Bible is an umimpeachable and totally authoritative source...(which I was not)...then they will probably interpret its writings as the absolute truth. I don't. I don't consider any book to be the absolute guaranteed truth, but a given book may still be quite useful as a guide toward part of the truth. Whether it is or not, that's a matter of individual opinion, or anyone's best guess.

The only thing that is an absolute guaranteed guide to the whole truth is life itself.