"Cyberspace. A consensual hallucination experienced daily by billions of legitimate operators, in every nation, by children being taught mathematical concepts... A graphic representation of data abstracted from the banks of every computer in the Human system. Unthinkable complexity. Lines of light ranged in the nonspace of the mind, clusters and constellations of data. Like city lights, recedding..."
Excerpt from William Gibson's Neuromancer.
L'esprit de l'escalier
This name for the phenomenon comes from French encyclopedist and philosopher Denis Diderot's description of such a situation in his Paradoxe sur le comédien. During a dinner at the home of statesman Jacques Necker, a remark was made to Diderot which left him speechless at the time, because, he explains, "l.homme sensible, comme moi, tout entier à ce qu.on lui objecte, perd la tête et ne se retrouve qu.au bas de l.escalier" ("a sensitive man, such as myself, overwhelmed by the argument levelled against him, becomes confused and can only think clearly again [when he reaches] the bottom of the stairs"). In this case, .the bottom of the stairs. refers to the architecture of the kind of hôtel particulier or mansion to which Diderot had been invited. In such houses, the reception rooms were located on the étage noble, the noble story, one floor above the ground floor, so that to have reached the bottom of the stairs means to have definitively left the gathering in question.
Diderot's fellow-philosophe Jean-Jacques Rousseau also recognised his own affliction with l.esprit de l.escalier. In his autobiographical book Confessions he blamed such social blunders and missed opportunities for turning him into a misanthrope, and reassured himself that he was better at "conversations by mail".
American English speakers sometimes also call this "elevator wit".