Find the pressure in the sentence
百折不挠 contains the idea of being bent many times without yielding. The sentence should show rejection, failure, resistance, or another pressure that makes recovery meaningful.
锲而不舍 focuses on not stopping the carving. The work can be difficult without a dramatic sequence of defeats.
Do not reward useless repetition
Neither phrase praises stubborn repetition after evidence shows that the method is harmful or irrelevant. Persistence can include changing the method while keeping the goal.
Describe the adaptation when it matters so the chengyu does not become a substitute for judgment.
Build evidence before praise
Name the attempts, setbacks, practice, revision, or recovery before adding the idiom. This keeps formal praise proportionate and natural.
Use plain Chinese or English when the context has not established the full pattern.
Compare the timeline
百折不挠 often compresses a series of blows and recoveries. 锲而不舍 can describe a steadier timeline in which a person continues a relevant practice even when progress is slow.
A long duration alone does not choose the phrase. Ask whether the reader should notice adversity or continuity.
Control the social force
Both expressions are formal praise and can sound inflated when attached to a minor routine task. In feedback, name the work first and place the chengyu after the evidence.
When speaking about another person's hardship, avoid turning pain into an inspirational label they did not choose. Plain acknowledgment may be more respectful.
Translate without erasing the difference
Resilient under repeated setbacks is often closer to 百折不挠. Kept at it or persevered is often closer to 锲而不舍. The surrounding sentence may need a longer translation to preserve the contrast.
Do not translate both automatically as never give up. That slogan removes the distinction between recovering from resistance and sustaining a relevant action.
A short editing exercise
Write a two-sentence example before choosing the chengyu. In the first sentence, name the action, obstacle, timeline, and observable result in plain language. In the second, add only one compact phrase and explain which part of the evidence it summarizes. This order prevents the idiom from doing work the facts have not earned.
Now test a near neighbor. Replace the chosen phrase and ask what becomes inaccurate: the kind of obstacle, the repeated action, the time pattern, the degree of surprise, or the social tone. Keep the original only when the contrast is visible to a reader who has not memorized the story. If both phrases still seem equally plausible, add context or use plain wording rather than pretending the distinction is settled.