Socrates, it is said, said that his wisdom consisted in the fact of his knowing nothing, and specifically in the knowing the fact of his knowing nothing. He was aware of his own ignorance and that this was what raised him above everyone else; that by contrast they weren't aware of their own ignorance; were labouring under the delusion of knowledge and inhabiting false certainties, and it seems to have been something of a personal mission of his to make them aware of this ignorance.
However if Socrates knew he knew nothing, then the one thing he thought he knew he didn't actually know, as to know anything, such as the knowing of nothing, is to know something, not nothing. To know one knows nothing is obviously a self-contradictory claim.
So he didn't know nothing but something, but the something he thought he knew he didn't even actually know, so in truth perhaps he was right after all: he did know nothing, or rather, he didn't know anything, not that he could know this without contradicting the not knowing of anything. So it transpires that the wisdom in which he imagined his wisdom solely to consist was delusional, imaginary. Which is ironic. And anyway, how could one know nothing? Nothing, since it doesn't exist, isn't something one could know. Knowledge involves knowledge about something, not nothing.
If someone like Socrates but a bit wiser had been around to accost him, in the manner of himself, and engage him in such a cross-examinination of his knowledge, he could have made him look a right fool.
A possibly amusing, possibly related notion:
A man was engaged in discussion with himself. He was convinced of his own madness. "I am mad," he would tell himself. "Ah but if I really was mad I wouldn't be aware of the fact. I would be convinced as to my not being mad. And so my being aware of being mad must mean I am not mad after all."
He was delighted with himself and his cunning. He had outsmarted them all.