Kural - 534

'To cowards is no fort's defence'; e'en so
The self-oblivious men no blessing know

Explanation
Just as the coward has no defence (by whatever fortifications ha may be surrounded), so the thoughtless has no good (whatever advantages he may possess).

Tamil Transliteration
Achcha Mutaiyaarkku Aranillai Aangillai
Pochchaap Putaiyaarkku Nanku.