自毀長城 [－毁长－]

Jyutping zi6 wai2 zoeng2 sing4
Pinyin zì huǐ cháng chéng

Definitions (Wiktionary)

phrase, idiomatic
to weaken oneself; to destroy one's own advantages or accomplishments

Jyutping zi6 wai2 coeng4 sing4
Pinyin zì huǐ cháng chéng

Definitions (粵典–words.hk)