Hawzah News Agency – Imam Ali (AS) said to Imam al-Hasan (AS):

إنّما قَلْبُ الحَدَثِ كالأرضِ الخالِيةِ ما اُلقِيَ فيها مِنْ شي‏ءٍ قَبِلَتْهُ، فبادَرْتُكَ بالأدبِ قبلَ أن يَقْسُوَ قلبُكَ ويَشتغِلَ لُبّكَ.

'The heart of a youth resembles an empty land - it receives all that is thrown into it. This is why I have started to teach you good manners before your heart is hardened and your soul is preoccupied.'

Source: Nahj al-Balagha, Letter 31