Kural - 486

The men of mighty power their hidden energies repress,
As fighting ram recoils to rush on foe with heavier stress

Explanation
The self-restraint of the energetic (while waiting for a suitable opportunity), is like the drawing back of a fighting-ram in order to butt.

Tamil Transliteration
Ookka Mutaiyaan Otukkam Porudhakar
Thaakkarkup Perun Thakaiththu.