Kural - 728

Though many things they've learned, yet useless are they all,
To man who cannot well and strongly speak in council hall

Explanation
Those who cannot agreeably speak good things before a good assembly are indeed unprofitable persons inspite of all their various acquirements.

Tamil Transliteration
Pallavai Katrum Payamilare Nallavaiyul
Nanku Selachchollaa Thaar.