Kural - 489

When hardest gain of opportunity at last is won,
With promptitude let hardest deed be done

Explanation
If a rare opportunity occurs, while it lasts, let a man do that which is rarely to be accomplished (but for such an opportunity).

Tamil Transliteration
Eydhar Kariyadhu Iyaindhakkaal Annilaiye
Seydhar Kariya Seyal.