Kural - 637

Though knowing all that books can teach, 'tis truest tact
To follow common sense of men in act

Explanation
Though you are acquainted with the (theoretical) methods (of performing an act), understand the ways of the world and act accordingly.

Tamil Transliteration
Seyarkai Arindhak Kataiththum Ulakaththu
Iyarkai Arindhu Seyal.