Someone, who have not understood that 'pain' can be feigned under such-and-such circumstances have not understood our concept of 'pain' at all. The possibility of pretence is a structural possibility, in a sense; a necessary possibility. And yet, the language game of 'pain' is not founded on the constant possibility of pretence and doubt, but on the actual presence of pain.
Language games must be regarded as essentially functioning, not as essentially defect. Scepticism bypasses this point; and this is the error of scepticism. Our language is alright as it is.
And as they are, our language games already includes the standard sceptical possibilities; and so the sceptic cannot be viewed as a revisionist, but only as someone who misconstrues our language game, as someone who lays the accent on the wrong part of our language game. But, of course, he is not laying the accent on a non-existing part of our language game; we do doubt each other and we do contest matters of fact.
That we accept more than we contest constitutes what Heidegger called our being "in tune". And so the sceptic tests the extent to which we are in tune. He is not a truth-seeker or a revisionist, but rather someone who tests our bond. The sceptic serves, as it were, a social function.