精於

精 = 米 + 青 : Joan of Arc scoops a bit of water from the fountain of youth in front of the engine and pours it into a bowl of rice. The water refines the rice into rice wine, and as Joan of Arc drinks it, she finds her spirit renewed.

于 = 亅 + 二 : Mnemonic symbol: prepositions (in, at, on, to, ...) are what glue the sentence together. Honey is as sticky as glue, so I'll represent 于 by a honey jar.

Yu the Great (于) was assigned to repair the electronics of the space station's kitchen (Ø2), but instead he was snacking honey from a honey jar (于). Unfortunately his capacitor (二) got stuck in the honey and now he has to use a crowbar (亅) to lever it out.