Authority is a commonly respected and undoubtful source since it has in its favor the factor of pressure. When someone we respect or think that knows a lot establishes something as true we are subconsciously influenced to believe in it. A clear example is a psychological experiment that was held in order to prove the strength of authority. A group of science students were given instructions by their teacher in order to accomplish an experiment that consisted in combining some gases. The combination of these actually led to the creation of a very powerful bomb. Even though a large majority of the students knew or at least suspected the reaction of this specific combination they had so much respect and credibility towards their teacher that they were actually going to do the experiment until they were told not to. From this example I can deduct as I already mentioned that people should consider knowers as a reliable source but not be blinded by them and try to think by themselves in order to reach their own truth. Sometimes although we respect and value a person's opinion we feel deep inside that what they are saying is not entirely correct. Instinct or emotions are other ways of acquiring knowledge and as in any source they don't always lead to truth but they should also be taken into account. Blaise Pascal says, "The heart has reasons Reason does not know-. Sometimes things that seem irrational are true and feelings may be stronger than reason and knowledge may be acquired by them. Reason is another path that can lead to truth, sometimes although a knower establishes something as true if we don't think it makes sense, if it's not reasonable we won't accept it as such.
Authority, represented in this specific case by the knower, is an extremely strong source. It is difficult to stand up to something you believe when someone who supposedly knows everything about the matter says that something is true even if you are sure and can prove it isn't.