Kural - 674

With work or foe, when you neglect some little thing,
If you reflect, like smouldering fire, 'twill ruin bring

Explanation
When duly considered, the incomplete execution of an undertaking and hostility will grow and destroy one like the (unextinguished) remnant of a fire.

Tamil Transliteration
Vinaipakai Endrirantin Echcham Ninaiyungaal
Theeyechcham Polath Therum.