"Who is in search of the truth? And what does the man who says "I want the truth" mean? Proust does not believe that man, nor even a supposedly pure mind, has by nature a desire for truth, a will-to-truth. We search for truth only when we are determined to do so in terms of a concrete situation, when we undergo a kind of violence that impels us to such a search."
Deleuze, Proust and Signs.
"There is always the violence of a sign that forces us into the search, that robs us of peace."
What kind of ‘signs’ are these? Not ones that immediately bare their signified. With the Proustian sign we intuit that it signifies without knowing what it signifies, and this delay and opacity between that and what is what incites the desire for truth.
You will say this is a familiar enough Deleuzian theme: the pursuit of truth, or thinking itself, is prompted always by a shock from outside thought altogether, a shock which puzzles and 'forces' thinking, and that Deleuze has simply read this ‘into’ Proust. But I wonder whether it isn't the other way around, and whether Deleuze doesn’t, at least partly, first learn this concept from Proust, as he seems to learn or generate so many of his concepts from literature (at least before his own thinking arguably ossifies into an endlessly repeated ensemble of concerns).
n.b., the distinction between that it signifies and what it signifies is taken up in a psychoanalytic context by Jean Laplanche, and also, very productively, by Eric Santner. (One of Santner's talks is available online here)