明哲保身

From the Classic of Poetry, poem 260 (《詩經·大雅·烝民》):

既明且哲，以保其身。
夙夜匪解，以事一人。 [Pre-Classical Chinese, trad. and simp.]

From: The Classic of Poetry, c. 11^th – 7^th centuries BCE, translated based on James Legge's version

Jì míng qiě zhé, yǐ bǎo qí shēn.
Sùyè fěi xiè, yǐ shì yīrén. [Pinyin]

Intelligent is he and wise, Protecting his own person.
Never idle, day or night, In the service of the One man.

明哲保身

1. to protect or defend oneself with wisdom and sound judgement
2. to protect oneself above all other considerations; to place one's own interests at the foremost

As a chengyu, its connotation has gradually shifted away from the literal meaning. Sense #2 carries the connotation that protecting one's self-interest (保身) is the "wisdom" referred to by 明哲, and its use implies indifference, lack of altruism, unwillingness to take risk, etc., all of which are reckoned wise practices.