My question is, would you prefer a friend's wounds to an enemy's kisses? Anyone who can, is considering the source. A friend has your best interest at heart. They may have to give you unpleasant advice at times, but you know it is for your own good.
Now an enemy on the other hand, may whisper sweet words and compliments that will eventually send you to ruin. Sad, but true, we tend to hear what we want to hear, even if an enemy is the only one saying it. When a leader listens to the flattery of an enemy, or unfaithful friend, not only the leader suffers but also those who follow him.
The words of a true friend, no matter how painful, are much better. Always consider the source, and the motive behind the words.