Hawzah News Agency – The commander of the faithful, Imam Ali peace be upon him says:

ما العَدُوُّ إلى‏ عَدُوِّهِ أسْوأَ تَضْيِيعاً مِن الأحمَقِ إلى‏ نَفْسِهِ

'A person does not ruin his enemy worse than a fool ruins himself.'

Source: Nahj al-Sa'ada, v. 3, p. 225