Believing things on authority only means believing them because you have been told them by someone you think trustworthy. (Historical events, scientific facts, medical explanations etc.) We believe them simply because people who did see them have left writings that tell us about them.
Mere Christianity – C. S. Lewis (1952)
What always concerns me when a piece of information is imparted is that I often have no way of ascertaining the validity of either the statement of the source from which it came. Whilst I might totally trust the person that is imparting it to me there is never any means of verifying where it came from in the first instance.
Chinese Whispers: a game where a sentence is whispered one person to another around a circle. Whilst the individual players do not blatantly lie, the result is often that the words are misheard, and therefore the sentence is changed by the time it is relayed to the last person.
This can be the same with all oral accounts, whether it be throughout history or simply idle gossip.
Also, the mere fact that something is committed to ink does not confirm that it is a true account of the facts. To imply that what is written is believable simply because it has been written down by someone, and therefore can then be taken as a first-hand account is not correct as it does not take into consideration books of non-fiction. The worlds of magic, the alternative universes, the accounts of historical events often told through the eyes of a peripheral participant. These books, if equated to that premise recount untruths, the doctrines of facts and nothing more than the vividness of an active imagination.
Oh, to be a fly-on-the-wall if in thousands of years’ time those manuscripts are unearthed.