Intro: This week’s saying is almost a synonym with last week’s 蛇の道は蛇.

餅は餅屋
(Mochi wa mochiya; “The mochi-maker [knows] mochi”)

Definition:

For the best mochi, go to a mochi-maker (instead of trying to make your own, or depending on the work of an amateur). If you need work done in a given field, it’s best to ask a specialist in that field. No matter how devoted or skillful an amateur or hobbyist is at a given task, they won’t be as good as a professional or specialist. In a way, this kotowaza is one of the fundamental underpinnings of modern economics: efficiency and improved results through specialization. It’s the inverse of “Jack of all trades, master of none.”

Breakdown:

Only two nouns and a particle in this one; it’s a phrase rather than a full sentence. 餅 (mochi) is a rice cake; 餅屋 (mochiya) is a rice-cake shop, maker, or seller. は (wa) is the topic-marker particle. Put them together and you get “As for rice cakes, rice-cake-shop.”

Notes:

What is mochi? It’s a cake – a lump, if you’re not feeling generous – of glutinous white rice that has been cooked and then pounded (traditionally with a wooden hammer in a large stone mortar that has been polished smooth on the inside) until it’s a single mass. Mochi may be eaten warm on the spot or saved; dried bricks for soup can even be bought in Japanese supermarkets. It may be eaten as-is; flavored with bean paste, kinako powder, or other sweet fillings or toppings; or toasted and eaten with soy sauce and other savory flavorings.

Example sentence:

「さすがに餅は餅屋で、グラフィック・アーティストが想像以上に素敵なロゴマークを描いてくださった」

(“Sasuga ni mochi wa mochiya de, gurafikku aatisuto ga souzou ijou ni suteki na logomaaku wo egaite kudasatta.”)

[“You really do need a specialist for some things; the graphic artist drew us a better logo than I imagined.”]