好自為之

Initially from Huainanzi – see quote below.

好自為之

1. (original meaning, literary, archaic) to like to do everything him/herself in one's own way

   • 君人者不任能而好自為之，則智日困而自負其責也。 [Traditional Chinese poetry, trad.]
     君人者不任能而好自为之，则智日困而自负其责也。 [Traditional Chinese poetry, simp.]

     From: Huainanzi, 2^nd century BCE

     Jūn rén zhě bù rèn néng ér hào zì wéi zhī, zé zhì rì kùn ér zì fù qí zé yě. [Pinyin]

     If the monarch does not appoint the capable but rather likes to handle the matters by himself, his intelligence will be increasingly exhausted and he will bear the consequences himself.

好自為之

1. (early modern, now rare) to do one's best; to endeavour to do something
2. (more common meaning nowadays, as a threat or admonition, derogatory) [You] better behave yourself, otherwise [you] will be in trouble! / You better watch out for yourself! You have been warned!