Kural - 108

'Tis never good to let the thought of good things done thee pass away;
Of things not good, 'tis good to rid thy memory that very day

Explanation
It is not good to forget a benefit; it is good to forget an injury even in the very moment (in which it is inflicted).

Tamil Transliteration
Nandri Marappadhu Nandrandru Nandralladhu
Andre Marappadhu Nandru.