不足为凭 Not enough to rely on
Explanation
不能作为凭据或根据。指证据、言论等不足以让人相信或采信。
Cannot be used as evidence or basis. Refers to evidence, statements, etc., that are not sufficient to make people believe or accept.
Origin Story
话说唐朝时期，一位名叫李白的诗人，才华横溢，名满天下。一日，李白与友人畅饮，酒酣耳热之际，李白信誓旦旦地说自己曾与神仙有过一面之缘，并描述了神仙的容貌、衣着，以及神仙洞府的奇景。友人听得啧啧称奇，半信半疑。然而，李白所说，全凭个人臆想，缺乏确凿的证据，不足为凭。 后来，李白的友人便将此事四处宣扬，说李白曾与神仙相会，绘声绘色地描述着李白所言。一时间，李白与神仙相会的故事传遍了大江南北，人们对李白的说法更是深信不疑。 然而，真相如何，却无人知晓。或许李白真的见过神仙，也或许只是他酒后的一场幻觉。但无论如何，李白的故事告诉我们，任何事情，都必须有确凿的证据才能令人信服。不足为凭的言论，只能是空中楼阁，经不起时间的考验。 又过了许多年，后世学者对李白的生平进行了深入研究，他们发现，李白所谓的“与神仙相会”的故事，其实是他为了增添自己的神秘色彩而杜撰出来的。这个故事，不足为凭，却也成为后世传颂的一个佳话。
During the Tang Dynasty, there was a famous poet named Li Bai, whose talent and fame were widespread. One day, while celebrating with friends, Li Bai swore that he had once met a god and described the god's appearance, clothing, and the wondrous scenes of the divine palace. His friends were astonished and half-convinced. However, Li Bai's description was based solely on his imagination and lacked concrete evidence, thus rendering it unconvincing. Later, Li Bai's friends spread this story, exaggerating Li Bai's account of meeting a god. In a short time, the story spread throughout China, and people firmly believed Li Bai's narration. However, nobody knew the truth. Perhaps Li Bai had indeed met a god, or it was just a drunken hallucination. Whatever the case, Li Bai's story shows us that any matter needs substantial evidence to be credible. Unbelievable claims are mere castles in the air, unable to withstand the test of time. Many years later, scholars thoroughly investigated Li Bai's life and found that the story of his encounter with a god was actually a fabrication to enhance his reputation. This unbelievable story nevertheless became a well-known anecdote.
Usage
用于评论证据、言论等缺乏可靠性，不足以采信。
Used to comment that evidence, statements, etc., lack reliability and are not credible.
Examples
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他的证词不足为凭，不能作为定案的依据。
tā de zhèngcí bù zú wéi píng, bù néng zuòwéi dìng'àn de yījù
His testimony is not credible and cannot be used as evidence for conviction.
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这些传闻不足为凭，我们不能轻信。
zhèxiē chuánwén bù zú wéi píng, wǒmen bù néng qīngxìn
These rumors are not credible; we cannot easily believe them.