Kural - 831

What one thing merits folly's special name.
Letting gain go, loss for one's own to claim

Explanation
Folly is one (of the chief defects); it is that which (makes one) incur loss and forego gain.

Tamil Transliteration
Pedhaimai Enpadhondru Yaadhenin Edhangontu
Oodhiyam Poka Vital.