In his Gorgias dialogue, Plato engages with Gorgias' sophistry, which the famous sophist is said to praise as the art of being able to exercise power over men's opinions and actions through rhetorical skill. It is allegedly the highest social power because the orator skilled in rhetoric needs no other power than the power of persuasion to exercise power over men with all sorts of other skills and powers.
Plato will have none of this, and calls rhetoric a mere "knack". He defends philosophy instead as the quest for truth rather than as a skill to exercise social power, thus initiating the struggle against sophistry that, to the present day, stands for the superiority of persuasive talk as the ultimate social power over the quest for truth. There is no denying that, in its guises as the talk of politicians and advertising, the power of rhetoric is indeed an uncanny, deftly deployed power on the surface of social life that, especially in today's mass societies, easily trumps the philosophical quest for truth.
But what is this philosophical quest for truth? The Greek word for truth is _alaetheia_ (ἀλήθεια), whose alpha prefix signifies a negation, namely, of _laethae_ (λήθη), whose standard English translation is 'oblivion' but, in this context, is more appropriately rendered as 'obscurity' or 'concealment'. At first, the phenomena do not show themselves as they are in themselves, but obscurely, distortedly, which results in their being misunderstood, misconceived by our mortal minds. (Note that this distortion does not pertain merely to being deceived by the senses.)
Hence we can say that 'at first and for the most part' (a phrase often used by Aristotle), we mortals exist in untruth, in distortions and misconceptions of the phenomena themselves. The truth of phenomena themselves is not merely about the correctness of facts (factual truth), because facts presuppose already a conception or misconception of the phenomena to which they refer. E.g. whether someone has committed a crime has to be brought to light by uncovering and presenting the facts of the matter to a court of law. Whether the act is a crime is not merely a matter of assessing it factually in terms of correspondence or non-correspondence to (i.e. infringement of) positive law, but depends on the conceptions of justice and freedom per se of the given society in an historical time on which the laws depend. Such conceptions or concepts may be called ideas (ἰδέαι) in Plato's sense, whose truth, Plato says, may be disclosed by _anamnaesis_ (ἀνάμνησις), i.e. remembrance or calling back (ἀνά) to mind (μένος), thus overcoming λήθη (oblivion, concealment). We mortals always already implicitly have in mind the ideas that mentally structure the world, but still have to call them explicitly to mind through philosophical questioning to see them clearly.
That makes of philosophy's quest for truth a struggle to wrest the truth from obscuring distortion and concealment. The distortion and concealment, in turn, reside in our very own misconceptions of the phenomena, which makes of philosophical endeavour a struggle with our own minds to clear away (at least some of) our misconceptions. This struggle to interpret the phenomena themselves starts with the most elementary, and therefore most consequential and decisive, ones, because they stand at the beginning (ἀρχή) of any attempt to think through the ideas through which the mind interprets the world.
The hermeneutic truth of certain phenomena themselves, i.e. their idea, may be uncomfortable and unwelcome. Because there are vested interests in maintaining certain elementary misconceptions for the sake of shoring up the status quo (the mind suffers from conservative inertia), the philosophical quest becomes also a socio-political struggle. Here the idea of freedom itself is pivotal: Wherein does human freedom consist? And the question concerning human freedom (a certain kind of movement) presupposes that we understand, i.e. interpret as best we can, who we are as humans. The question of the truth of human being itself, if it is raised at all, rather than being ignored, suppressed or answered by well-worn clichés, is a struggle, perhaps an ultimate one, to clear away the misconceptions and bring the truth to light. This truth is an hermeneutic one for an historical time.
Further reading: On Human Temporality.