Kural - 279

Cruel is the arrow straight, the crooked lute is sweet,
Judge by their deeds the many forms of men you meet

Explanation
As, in its use, the arrow is crooked, and the curved lute is straight, so by their deeds, (and not by their appearance) let (the uprightness or crookedness of) men be estimated.

Tamil Transliteration
Kanaikotidhu Yaazhkotu Sevvidhuaang Kanna
Vinaipatu Paalaal Kolal.