《资治通鉴·齐纪·齐纪六》
堵水要先塞住水源，伐木要先断其根本，如果本源尚在而只攻其末流，到底也不会有什么成效的。
夫壅水者先塞其原，伐木者先断其本；本原尚在而攻其末流，终无益也。
To block the water, you must first block the source; to cut down a tree, you must first cut its roots. If the root is still there and you only attack its branches, it will not be effective.