不知天高地厚
bù​zhī​tiān​gāo​dì​hòu

to have an exaggerated opinion of oneself

  1. 不知 bù​zhī verb
    not to know
    to not know; to be unaware of or have no idea about
  2. 天高地厚 tiān​gāo​dì​hòu
    complexity of things
    (idiom) the complexity and vastness of the world or reality, often used in the phrase 不知 bù​zhī tiān gāo dì hòu to describe a young or arrogant person who is unaware of the consequences of their actions