Kural - 611

Say not, 'Tis hard', in weak, desponding hour,
For strenuous effort gives prevailing power

Explanation
Yield not to the feebleness which says, "this is too difficult to be done"; labour will give the greatness (of mind) which is necessary (to do it).

Tamil Transliteration
Arumai Utaiththendru Asaavaamai Ventum
Perumai Muyarsi Tharum.