"Who can boast," we read in The Lottery of Babylon, "of being a mere imposter?" The suggestion is not that we can't boast about being imposters if we feel like it, and not that we can't, on occasion, actually be imposters, only that we can't be sure of being imposters, even when we think we are. We can't, that is, entirely rely on our falsehoods, we can't guarantee that truth will not catch up with us, or catch us out. This proposition is the mirror image of [...] that form of feigning or counterfeiting which is never entirely safe from the charge of simply lying. Here is a form of lying which is never entirely safe from the charge of telling the truth.
The truthful imposter is the figure who wrecks Austin's picture of the parasitic performative utterances and the etiolations of language. He is the man who thinks he is a bigamist but turns out to have been divorced without his knowledge and so finds himself acting in good faith against his own will and awareness. He thinks he is in a play or poem, in this case of his own devising, but he's not.
In literature it takes only one truthful imposter to put the very idea of the 'normal' to flight. What literature knows is how vulnerable we are to what Henry James called 'operative irony': 'It implies and projects the possible other case.' Resisting the thought of this other case may seem like mere sanity, and often is; but resisting it all the time is going to look like an expression of fear.