(Narau yori nareyo; “Experience over learning”)
It’s easier to acquire knowledge or learn a skill by practicing it firsthand than through simply being taught. Hands-on study beats abstract learning methods like lectures or book-reading.
We have two verb phrases and a particle here, yet it’s still a full sentence! The first verb is 習う (narau), “to study,” “to learn (from a teacher).” The verb is in prenominal form so that it can be followed by the particle より (yori), “more than,” “rather than.” The particle points to, and thus devalues, 習う in favor of the following verb, 慣る (naru), which appears in imperative form. (Note that the modern “base” form of this verb is not 慣る but 慣れる, nareru.) Note that while the imperative form makes this phrase into a command rather than an assertion, I’ve mostly heard it used tangentially rather than directed at someone with imperative intent.
The modern imperative form of the second verb, 慣れろ, may also be used. (For that matter, 習う is the modern form of a verb that would previously have been 習ふ, but that’s more a matter of orthography than grammar.)
I’ve had a number of discussions about this idea in a pedagogical context, and my first impulse is to become annoyed at people who undervalue or even scornfully reject classroom learning: an organized, theory-based course of study can be invaluable for most people in learning most topics, even practical manual skills! That said, clearly a balance is best. These days, even our most abstract ideas, such as mathematics and philosophy, tend to be taught with hands-on methods like homework problems or group discussion of ethics problems. So I’d say that in the end, there is no true conflict. You get a book or a teacher, or both, to make concepts or skill sets accessible, and then you get personal experience in order to make them stick.
(“Hyakuten manten de hikki shiken ni goukaku shite mo, jisshi shiken ni ochitara yappari unten dekinain da yo. Narau yori narero to iu kara, unten no renshuu mo ganbatte!”)
[“Even if you got a perfect score on the written test, of course failing the practical means you can’t drive! As they say, you learn by doing, so get out there and practice!”]