How did 'litotes' evolve from 'plain, simple'?

Question

litotes (n.)
rhetorical figure in which an affirmative is expressed by the negative of its opposite, from Greek litotes, literally "plainness, simplicity," from litos "smooth, plain, small, meager,"
from PIE root *(s)lei- "slimy, sticky, slippery" (hence "smooth"); see slime (n.).

Litotes adds (negative) words and so increases reading time. So how did it evolve from litos "smooth, plain, small, meager", adjectives all of which contradict the troubles of hypernegation?

I thought about the interpretation of hypernegation as slimy, which would consist with the PIE root. But this guess appears wrong, because PIE is invented and so succeeds Greek.

Answer 1

It's a value judgement, clearly. To be litos is to be plain as a positive value judgement; cf. English "plain-spoken". Plainness of speech was extended to avoiding superlatives in speech, as excessively emotive: Ancient Greek culture valued "moderation", which includes understatement. Saying something is "not uncommon" or "not ungraceful" increases processing time, but the praiseworthy plainness from an Ancient Greek perspective is not about processing simplicity (and reading isn't really the point here—these were conventions of oratory). The praiseworthy plainness is about making a show of being reluctant to go overboard in one's positive descriptions.

That's speculation based on what I know of Greek and Ancient Greeks. While https://en.wikipedia.org/wiki/Litotes reports that the rhetorical figure is already in place in Homer, LSJ reports that the earliest use of litotes to describe it is in late Roman grammarians: https://en.wikipedia.org/wiki/Maurus_Servius_Honoratus' commentary on Virgil, https://en.wikipedia.org/wiki/Aelius_Donatus' commentary on Terence (4th to 5th centuries AD.)