Also from Section XII the same issue of knowledge is explained by Cicero:
QuoteThen I replied — Arcesilas, as we understand, directed all his attacks against Zeno, not out of obstinacy or any desire of gaining the victory, as it appears to me, but by reason of the obscurity of those things which had brought Socrates to the confession of ignorance, and even before Socrates, Democritus, Anaxagoras, Empedocles, and nearly all the ancients; who asserted that nothing could be ascertained, or perceived, or known: that the senses of man were narrow, his mind feeble, the course of his life short, and that truth, as Democritus said, was sunk in the deep; that everything depended on opinions and established customs; that nothing was left to truth. They said in short, that everything was enveloped in darkness; therefore Arcesilas asserted that there was nothing which could be known, not even that very piece of knowledge which Socrates had left himself. Thus he thought that everything lay hid in secret, and that there was nothing which could be discerned or understood; for which reasons it was not right for any one to profess or affirm anything, or sanction anything by his assent, but men ought always to restrain their rashness and to keep it in check so as to guard it against every fall.
For rashness would be very remarkable when anything unknown or false was approved of; and nothing could be more discreditable than for a man's assent and approbation to precede his knowledge and perception of a fact. And he used to act consistently with these principles, so as to pass most of his days in arguing against every one's opinion, in order that when equally important reasons were found for both sides of the same question, the judgment might more naturally be suspended, and prevented from giving assent to either.