It is Proust's great recurrent theme: your voluntary memory is restrained by facts and by common sense, all misleading when you try to recall a distant past. He gives Ambassador Norpois' old-fashioned language as an example. Proust had to re-create it to make it come to life in his novel:
“Norpois' conversation was such a collection of outdated formulas that I often regret I did not simply write down the things he said..
That way, I could now produce an effect of retro decor as easily as that actor who was asked where he managed to find his surprising hats, and he answered: "I keep them."
Shortened and simplified from a free e-text at http://intexto.org/opus/en/proust/recherche/014 quoted below
I should add that his conversation furnished so exhaustive a glossary of the superannuated forms of speech peculiar to a certain profession, class and period [....]that I sometimes regret that I have not simply kept any literal record of the things that I have heard him say. I should thus have obtained an effect of old-fashioned courtesy by the same process and at as little expense as that actor at the Palais-Royal who, when asked where on earth he managed to find his astounding hats, answered, “I do not find my hats. I keep them.”
The French original:
Et je dois dire que la conversation de M. de Norpois était un répertoire si complet des formes surannées du langage particulières à une carrière, à une classe, et à un temps — un temps qui, pour cette carrière et cette classe-là, pourrait bien ne pas être tout à fait aboli — que je regrette parfois de n’avoir pas retenu purement et simplement les propos que je lui ai entendu tenir. J’aurais ainsi obtenu un effet de démodé, à aussi bon compte et de la même façon que cet acteur du Palais-Royal à qui on demandait où il pouvait trouver ses surprenants chapeaux et qui répondait : « Je ne trouve pas mes chapeaux. Je les garde. »In other words, in Proust's view, a novelist creates and does not copy. -- He doesn't keep old hats, but tries to call them up as pictures from his inners.