Tā quēfá zìzhī zhī míng, zǒngshì gāogū zìjǐ de nénglì.
He lacks self-awareness and always overestimates his abilities.
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From the Tao Te Ching (道德经) by Laozi: 「知人者智,自知者明」— 'Knowing others is wisdom; knowing oneself is enlightenment.' 自知之明 distills this into a four-character idiom emphasizing that self-knowledge is the highest form of wisdom.