expression
even the strong will grow weak
A classical Chinese-derived proverb (故事成語) meaning that even great power eventually fades and becomes ineffective. The literal image is that an arrow shot from a strong crossbow loses momentum and cannot pierce thin Lu silk. Used in formal or literary contexts to warn against overconfidence or to note the decline of once-mighty forces.
See also: 魯 (ろ)
かつての大国も今や強弩の末魯縞に入る能わずの状態だ。
Even the once-great nation is now in a state where its power has waned and can achieve little.
Also a proverb about the decline of the powerful, but 盛者必衰 is a Buddhist-derived phrase emphasizing the impermanence of all flourishing things, while 強弩の末魯縞に入る能わず focuses on the inevitable weakening of force or momentum.
From the Records of the Grand Historian (史記). The phrase originally described how even a powerful crossbow's arrow loses force over distance and cannot pierce thin silk. It entered Japanese as a 故事成語 (classical proverb).