自以為是

自以为是
zìyǐwéishì
  1. to believe oneself infallible (idiom)
  2. to be opinionated

CEDICT

Entry Composition

1 自 zì
  1. (bound form) self; oneself
  2. from; since
  3. naturally; as a matter of course
2 以為 yǐwéi to think; to believe (often with the implication that the belief is mistaken – unless referring to one's own current belief)
=3 是 shì
  1. to be (followed by substantives only)
  2. correct; right; true
  3. (respectful acknowledgement of a command) very well
  4. (adverb for emphatic assertion)
=3 是 shì variant of 是 shì