सिम्पाने ठिटो

नाद्रव्ये निहिता काचित्क्रिया फलवती भवेत् ।

न व्यापारशतेनापि शुकवत्पाठ्यते बकः ॥

-हितोपदेश

must not expend effort in trying to improve

something that does not deserve the efforts (or

simply can not change). No matter how hard you

try, you can not teach a duck the same tricks you

teach a parrot