石橋を叩いて渡る
(Ishibashi wo tataite wataru; “Striking a stone bridge and crossing”)
Definition:
Doubling and redoubling one’s precautions. Being extremely careful, especially in terms of safety. Like someone who comes to a sturdy stone bridge and still takes the time to test it by hitting it with a stick before crossing. This saying may be used positively, to encourage thorough vigilance, or negatively, to sarcastically criticize cowardice or unnecessary degrees of caution.
Breakdown:
We begin with compound noun 石橋 (ishibashi), “stone bridge.” The bridge is marked by the particle を (wo) as being the direct object of the verb 叩く (tataku), “to strike” – and also of the following verb 渡る (wataru), “to cross (over).” The first verb is in conjunctive form, so it can link to the second; the second is in sentence-final form, so it can end the sentence.
Notes:
Trivia of the day: Ishibashi is also the family name of the person who founded Bridgestone Tires.
This saying has a number of variations and spin-offs. 石橋 may be expanded from a compound noun to noun phrase 石の橋 (ishi no hashi), “a bridge of stone.” The final verb may appear in imperative form as 渡れ (watare). The need for caution may be emphasized by replacing を with も (mo) or でも (demo), “even.” Taking all possible precautions but not actually following through with action may be expressed by changing the noun structures to 叩いても渡らない (tataitemo wataranai), “doesn’t cross even after striking.” And taking so many precautions that the endeavor ends in failure as a result may be expressed by replacing the final verb with 壊す (kowasu), “to break.”
Example sentence:
普段は適当に食事を作ってほとんど無意識に一人で食べてきた晃が、初めて自分の家に招いた彼女のために石橋を叩いて渡るように、レシピを何度も読んで練習を重ねていた。
(“Fudan wa tekitou ni shokuji wo tsukutte hotondo muishiki ni hitori de tabete kita Akira ga, hajimete jibun no ie ni maneita kanojo no tame ni ishibashi wo tataite wataru you ni, reshipi wo nando mo yonde renshuu wo kasaneteita.”)
[“Akira normally threw together his meals and ate alone, barely paying attention. But now, having invited his girlfriend over for the first time, he was taking every precaution imaginable, reading and practicing the recipe any number of times.”]
landofnudotcom 
An osmotic balance of worries?
内憂外患
nai.yuu.gai.kan
Literally: inside – grieve – outside – affliction
Alternately: Troubles both within and from without (a country). Internal and external problems. For example, alienating both your populace and your neighbors. By extension, can refer to the combination of intra- and inter-entity problems for households, corporations, and so on.
Notes: Some versions replace 憂 with 患 and the second 患 with 禍 (ka, “misfortune”).
This compound comes to us from the Commentary of Zuo (『春秋左氏伝』, in Japanese Shunjuu sashiden), which we’ve seen before.
Japanese Prime Minister Abe, pummeled with internal scandals while being excluded from talks between the Koreas, China, and the USA.