No matter how well-intentioned, public speech from candidates on the campaign trail –or elected officials who are already in office– cannot ever be entirely sincere, but is something between being either a technology entirely for the purpose of securing political power (an anecdotal exhibit B of this here) or else is in some sense caught up into the gravity well of such a game, no matter how honest and authentic the politicians wish to be. (Even the honesty and “authenticity” of any given politician, insofar as these makes such a candidate attractive to an electing populace, become tools, instruments, means to gain power as soon as they enter into the political game.  Anyone watching recent popular TV shows recognizes this.) The game holds sway over what can and must be said in order to be successful, for success means persuasion and even domination according to the rules of the game, rather than the communication of truth. For Plato’s Socrates, however, true speech is not about control.
For Socrates, a philosopher should be always concerned with truth. Those who are interested in power are at a distance from this ideal, for they cannot be entirely so interested in truth: their pursuit of political office means that, to the degree that they as politicians are interested in truth, it must aid in their acquisition of, or retention of, power. Within a democratic polity, a principled and consistent concern with truth on the part of those in power will, at least at times, fight against the interests of those who are in power.
Plato, in his work The Republic, writes about this in Book Six in a section usually given (by editors and translators) “The Ship of State”. (Our idea of a “state” is not at all an exact equivalent to Plato’s understanding of a “regime” or a “city”, but it is good enough for now.) Professor David Roochnik of Boston University, in the supplementary materials from his online course on Plato’s Republic (available on Audible.com here), calls this parable “one of the most pessimistic interpretations of “real-world” politics ever conceived”, and summarizes it thus:
in normal cities, philosophers are few and far between and are usually disparaged by the general population. [Plato] expresses his view through a parable: that of the ship of state. The [city] is represented by a ship; the philosopher, by the “true pilot,” the one who really understands how to navigate the ship; the citizens are represented by the sailors, who instead of obeying the true pilot, fight to gain control of the rudder. As a result, the ship sails badly and does not succeed in reaching its destination.
There are videos about our excerpt, and about relevant themes and passages from Plato’s Republic. The BBC has a charming interpretation and summary of the passage here; Alain de Botton, in one of his School of Life videos, can be heard summarizing Plato’s concerns about the problems inherent in democracies here. As for non-video write-ups, a negative (mis?)take on Plato’s Socrates’ view in the spirit of Karl Popper and Bertrand Russel can be found here.
In his edition of The Republic, R. E. Allen translates our passage thus (I have modified Allen’s translation by adding quotes, changing the formatting slightly, and adding names in brackets for every time the speaker changes; the relevant page numbers of Allen’s edition appear in brackets that have been inserted into the cited text; I apologize only very, very slightly for dropping the reader into the middle of our text without warning or context):
 And Adeimantus said, “No one can gainsay you in this, Socrates. Still, when you talk this way, your hearers are often affected somewhat like this: they believe that through inexperience in question and answer, they are little by  little led astray by the argument at every question, and when the little mistakes are collected at the end, they turn out to be a big slip and opposite to what was said at first. Just as less skillful players at backgammon are finally shut out by clever ones and can’t make a move, so also they themselves are finally shut out in this other kind of game where the counters are not pebbles but words, and don’t have a thing to say — though it’s not at all the more true for being that way. I speak with a view to the present argument. For as it is, someone might say that he cannot oppose you on any given question in word, but he sees in deed, among those who turn to philosophy and continue in it too long instead of taking it up to complete their education while young and then dropping it, that the greater part become very strange, not to say rotten, and even those who seem best nevertheless become useless to their cities as an effect of the study you praise.”
[Socrates:] And I listened and said, “Well, do you think those who say this are mistaken?”
“I don’t know”, [Adeimantus] replied. “I’d gladly hear what you think.”
[Socrates:] “You would hear that they appear to me to tell the truth.”
“Then how can it be proper”, [Adeimantus] said, “to claim that cities will find no surcease from evils until philosophers –whom we agree are useless to them– rule in them?”
[Socrates:] “You ask a question”, I replied, “which needs an answer stated through an image.”
“I think you are not unaccustomed to speak through images”, [Adeimantus] said.
[Socrates:] “Well, well”, I replied. “You poke fun at me, after throwing me into an argument so hard to prove? Then hear the image, so that you may still better see how hard I strain to draw it. The experience of the best sort of men in relation to their cities is so difficult that nothing else is like it; to defend them by offering an image, one must collect it from many sources, as painters mix things up to draw goat-stags and such. Conceive this then as happening on many ships or one. A shipmaster is big and strong beyond everyone  else on board, but also a bit deaf and somewhat near-sighted; and his knowledge of navigation is like that too. The sailors quarrel with each other over the helm; each thinks he ought to steer though he has never learned the art and cannot point to a teacher or a time in which he learned. They claim in addition that navigation cannot be taught, and they are ready to cut to pieces anyone who claims it can. They crowd around the shipmaster, begging him, prepared to do anything if only he will turn the rudder over to them. Sometimes, if they do not persuade him, but others do, they kill them or throw them overboard and banish them. Using drugs or drink or something else, they bind the noble shipmaster hand and foot, seize the ship, plunder its stores, and sail on as one might expect, drinking and feasting. In addition, they praise and call a man a navigator, a pilot, and a master of seamanship if only he is clever at persuading or compelling the shipmaster to let them govern; anyone not like that they condemn as useless. They do not realize that a genuine pilot must be concerned with the year and its seasons, with sky and stars and winds and all that belongs to his art, if he really intends to be governor of a ship. Neither do they suppose that there is an art or study of steering, whether one wishes it so or not, nor that it is possible to grasp it and therewith the art of the pilot. When things like this occur, don’t you believe that sailors on ships managed this way will call the true pilot really a stargazer and an idle babbler, and useless to them?”
“Indeed”, said Adeimantus.
[Socrates:] “Then you understand what I mean”, I replied. “I doubt you need examine the image further to see that it is like the disposition of cities toward genuine philosophers.”
“Yes”, [Adeimantus] said.
[Socrates:] “Then first teach this image to anyone who is surprised that philosophers are not honored in their cities, and try to persuade him that it would be much more surprising if they were.”
 “Why, I will teach it”, [Adeimantus] said.
[Socrates:] “And further, that he is right to claim that the best among those in philosophy are useless to the multitude. However, he is not to blame good men for their uselessness, but rather those who make no use of them. For it is not natural that a pilot should beg sailors to be governed by himself, or for the wise to go to the doors of the rich; whoever invented that bit of cleverness was wrong. The actual truth is that, rich or poor, a sick man must go to the doors of doctors, and all who need to be ruled to the doors of someone capable of ruling; it is not for the ruler to beg those who need ruling to submit to being ruled, if he in truth confers a benefit. But you will not be mistaken in comparing present-day political rulers to the sailors we just described, and those whom they call useless babbling stargazers to true pilots.”
“Quite right”, [Adeimantus] said.
[Socrates:] “In consequence then, and under these conditions, the most noble pursuit is not easily held in high esteem by those who practice occupations opposed to it. But by far the greatest and strongest prejudice against philosophy arises through those who claim to practice it. The accuser of philosophy, you say, claims that most of those who go to her are thoroughly bad, and the best sort useless. And I conceded that is true, did I not?”
[Socrates:] “Then we have explained the cause of uselessness of the better sort?”
–and thus ends our passage.
Roochnik summarizes thus:
1. The city is like a ship, owned by someone ignorant of seamanship.
2. The sailors compete against one another in order to gain control of the ship (to gain the rudder).
3. The sailor who wins this competition becomes the pilot of the ship. (Kubernêtês, which is the root of our word governor, means “pilot.”)
4. But this pilot knows nothing about seamanship; he knows only how to gain control of the rudder (that is, political power).
5. The “true pilot” (489a) spends his time studying the stars, the weather patterns, and so on. He is, therefore, singularly ill equipped to compete against the other sailors for the rudder. The true pilot is destined never to be the actual pilot of the ship.
Or, as he also writes, “[the] pilot [who gains control of the ship] knows nothing about seamanship; he knows only how to gain control of the rudder”. Since “the true pilot”, the philosopher, invests his energies into the truth, he does not invest them into the game by which one gains control of the ship, with the result that he is doomed never to gain political control.
The same is true of marketing. See this image of Anthony Robbins meditating — the meditative act, even if it is here entered into, is subordinate to the end of making Robbins appear meditative, and so increase his public image, and so get him more followers and make him more money. The capitalist logic is inescapable: even if Robbins wants to help people by what he does, he must play this game to make money, and the game he must play to do this is necessarily corrosive on any social mission. This is not an argument against social missions, but it requires us to be honest with ourselves about the limits on our projects.
“489a” is a Stephanos number, found in the margins of any modern translation of Plato’s Republic or his other works, allowing people with different translations to find their way through the texts even if they don’t have the same page numbers, and allowing them to find the same passage in the surviving editions of the original Greek. I did not supply them for this excerpt. Allen has them in his text, as does every other English-language translation that I’ve seen.