Kural - 663

Man's fitting work is known but by success achieved;
In midst the plan revealed brings ruin ne'er to be retrieved

Explanation
So to perform an act as to publish it (only) at its termination is (true) manliness; for to announce it beforehand, will cause irremediable sorrow.

Tamil Transliteration
663, Kataikkotkach Cheydhakka Thaanmai Itaikkotkin
Etraa Vizhuman Tharum.