有口难辩 hard to defend oneself
Explanation
虽然有嘴，却难以辩解清楚，常指尽管事实并非如此，但难以解释清楚，让人误解。
Although you have a mouth, it's hard to explain clearly. It often refers to the situation where even if the facts are not so, it is difficult to explain clearly, leading to misunderstandings.
Origin Story
话说唐朝时期，有一个叫李白的诗人，他非常有才华，但是为人比较狂放不羁，得罪了不少达官贵人。有一次，他被卷入了一场宫廷斗争，被一些人诬陷为谋反。虽然李白据理力争，有口难辩，但仍然被捕入狱。在狱中，他写下了许多千古绝句，表达了他内心的委屈和愤懑。后来，在一些正直官员的帮助下，李白才被释放，然而这场冤狱，却给他留下了一生的阴影。
In the Tang Dynasty, there was a poet named Li Bai who was very talented, but also quite unrestrained and arrogant, offending many powerful officials. Once, he was involved in a court intrigue and framed for rebellion. Although Li Bai reasoned with all his might, he found it difficult to clear his name and was imprisoned. In prison, he wrote many immortal poems, expressing his grievance and resentment. Later, with the help of some upright officials, Li Bai was released, but the wrongful imprisonment cast a shadow over his life.
Usage
常用来形容人虽然有理，但难以解释清楚，导致别人误解，含冤莫白。
Often used to describe a situation where a person has a valid point, but cannot explain it clearly, leading to misunderstandings and wrongful accusations.
Examples
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他虽然百口莫辩，但事实胜于雄辩，最终还是被判了刑。
tā suīrán bǎikǒu mò biàn, dàn shìshí shèng yú xióngbiàn, zuìzhōng háishì bèi pàn le xíng。
Although he protested his innocence, the evidence was overwhelming and he was convicted.
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面对众人的指责，他感到有口难辩，只能默默承受。
miàn duì zhòng rén de zhǐzé, tā gǎndào yǒu kǒu nán biàn, zhǐ néng mòmò chéngshòu。
Faced with everyone's accusations, he felt speechless and could only silently bear it