Thirukkural – 540
To achieve what one has in mind is easy,
if he constantly has it in mind.
உள்ளியது எய்தல் எளிதுமன்-மற்றும் தான்
To achieve one’s aim is easy, if he constantly has his aim in his mind. Similar to Napolean Hill’s “whatever the mind can conceive and believe, it can achieve”. 2000 years earlier than Hill though.