昔齊人有欲金者，清旦衣冠而之市。適鬻金者之所，因攫其金而去。吏捕得之，問曰：“人皆在焉，子攫人之金何？”對曰：“取金之時，不見人，徒見金。” 

A dude in erstwhile State of Qi was coveting gold.  One early morning, he put on his clothes and hat and went to the marketplace, proceeding to a gold shop.  He then grasped some gold and run away.  An official captured him and asked him why he stole gold while other people were around.  That dude of Qi replied to the question that when he was robbing, there were nothing else but gold in his eyes.  

PS One of Chinese idioms can best describe such a stupid thing: 利令智昏