In today's society there is no shortage of teachers, each proclaiming to possess the truth in one form or another. One need only go to University or College to realize that such is the case. As is often the case with today's students, many people simply eat up everything they're given without giving a second thought to whether or not it is good for them. In the Protagoras, Socrates gives the following lesson to a young man, named Hippocrates, who wished to go hear Protagoras - a well-known Sophist.
"So if you are a knowledgeable consumer, you can buy teachings safely from Protagoras or anyone else. But if you're not, please don't risk what is most dear to you on a roll of the dice, for there is a far greater risk in buying teachings than in buying food....But you cannot carry teachings away in a separate container. You put your money down and take the teachings away in your soul by having learned it, and off you go, either helped or injured (313e-314b)."
Before simply buying into the teachings of any so-called teacher we need to be sure that the teacher is credible, and qualified, to teach on the subject at hand. Furthermore, we need to be sure that the teacher knows the subject that he is supposed to be teaching. One cannot give what one does not possess.