-The Flammarion Engraving, first documented in Camille Flammarion's 1888 book L'atmosphère : météorologie populaire
We live in a world full of errors & uncertainties, but that doesn't make knowledge impossible. The real problem is our intuition that 'true' always means getting to look behind the curtain - 'getting our homework marked by god'. When we think hard though, we find 'true' isn't in the 'facts', it is in the whole situation of evaluating them, and never stand separately from them.
-from this answer: Why is a measured true value “TRUE”?
I like the example 'opposites', of how we develop and use a 'language game', from simple to learn examples to very abstract cases: Life and Death as one and the same? The pairs are not unambiguous though, and the intuitiveness of the game can often cause us problems and contradictions. I like the elaboration of how we do this kind of thing, in Surfaces and Essences: Analogy as the Fuel and Fire of Thinking by Douglas Hofstadter and Emmanuel Sander.
Wittgenstein used the example of the word 'game' itself to demonstrate language-games, drawing attention with it to how a word can be intuitive and useful, even while we can't exhaustively and precisely define it. We feel we know people are engaged in a game when we see it. I feel he crystalises his point here:
"In this sort of predicament, always ask yourself: How did we learn
the meaning of this word ("good", for instance)? From what sort of
examples? In what language-games? Then it will be easier for you to
see that the word must have a family of meanings."
-Wittgenstein, in Philosophical Investigations
The Hilbert Programme to provide a finitistic proof of the consistency of the axioms of arithmetic, Lord Kelvin's alleged declaration in 1900
“There is nothing new to be discovered in physics now. All that
remains is more and more precise measurement.”
-supposedly from Royal Institution lecture Nineteenth-Century Clouds Over the Dynamical Theory of Heat and Light 27 April 1900, but at
best a gross paraphrase
and the modern discovery that we don't know what 95% of the cosmos is made out of, illustrate how our greatest progress has been from revelations of the scale of our ignorance, and as we have thought our job of understanding was nearly done we broke out into new vistas of uncertainty.
"I don't know X"
Consider the game of pointing, and a child using a finger in that game, to identify something as unknown to them. True? False? Meaningless? Those labels are irrelevant, because their use of the pointing game is likely effective. They have conveyed something, likely to someone that can give them information. How will the witness to the pointing answer? Many contextual cues and clues will be involved, in deciding what 'knowing' will be in this case. Likely they will both get meshed into the 'Why?' game, discussed here: "Why ask why" and its scions
Vervaeke has this nice term 'cognitive grip', that we look for handles on our knowledge of the world, that can help us manipulate that knowledge effectively, towards acting on the world. He relates that to the idea that knowledge is about building up 'salience landscapes', where we gain useful new information, by arranging facts/data/observations relationally between themselves and to ourselves. For instance, by situating ourselves in a meaning-cosmology, like the 'Why?' game leads to. Discussed more in this answer: According to the major theories of concepts, where do meanings come from?
We can't know what we don't know. But, we can situate ourselves effectively towards that:
"I seem, then, in just this little thing to be wiser than this man at
any rate, that what I do not know I do not think I know either."
-Socrates, in Plato's 'Apology'
Rumsfeld's famous declaration "There are unknown unknowns" is another example of such a situating. Science is always tentative, and in such a cautious and humble approach, we have found our deepest understandings.