For this reason, mixing with men is wonderfully useful, and visiting foreign countries […] to bring back knowledge of the characters and ways of those nations, and to rub and polish our brains by contact with those of others.

[A cette cause le commerce des hommes y est merveilleusement propre, & la visite des pays estrangers […] pour en rapporter principalement les humeurs de ces nations & leurs façons : & pour frotter & limer nostre cervelle contre celle d’autruy.]

Michel de Montaigne (1533-1592) French essayist
Essays, Book 1, ch. 25 (1.25), “Of the Education of Children [De l’institution des enfans]” (1579) [tr. Frame (1943), ch. 26]
    (Source)

Talking of education through practical experience, not simply book learning.

This essay and passage were in the 1st (1580) edition. Some translators use the 1588 sequence of chapters, not the 1595, and so identify this as ch. 26.

(Source (French)). Alternate translations:

For furtherence thereof, commerce or common societie among men, visiting of forraine countries, and observing of strange fashions, are very necessary [...] But they should principally observe, and be able to make certaine relation of the humours and fashions of those countries they have seene, that they may the better know, how to correct and prepare their wittes by those of others.
[tr. Florio (1603), ch. 25]

And for this reason, conversation with men is of very great use and travel into foreign countries; [...] to be able chiefly to give an account of the humours, manners, customs, and laws of those nations where he has been, and that we may whet and sharpen our wits by rubbing them against those of others.
[tr. Cotton (1686); Cotton/Hazlitt (1877), ch. 25]

And for this very reason the society of men, the visiting of foreign countries, observing people and strange customs, are very necessary; [...] They should be able to give an account of the ideas, manners, customs, and laws of the nations they have visited. That he may whet and sharpen his wits by rubbing them upon those of others.
[tr. Rector (1899), ch. 25]

For this reason, intercourse with men is wonderfully proper for [education], and travel in foreign countries, [...] chiefly to bring back the characteristics of those nations and their manner of living, and to rub and file our wits against those of others.
[tr. Ives (1925), ch. 26]

Human society is wonderfully adapted to this end, and so is travel in foreign countries [...] for the practical purpose of discovering the characteristics and customs of the different nations, and of rubbing and polishing our wits on those of others.
[tr. Cohen (1958), ch. 26]

For this purpose mixing with people is wonderfully appropriate. So are visits to foreign lands [...] mainly learning of the humours of those peoples and of their manners, and knocking off our corners by rubbing our brains against other people’s.
[tr. Screech (1987)]

For this reason social intercourse is wonderfully suitable for it, and visiting foreign countries [...] mainly to bring back the character of these lands and their ways and to polish and refine our brains by rubbing against the others'.
[tr. Atkinson/Sices (2012)]