Today's enemies can be your friends tomorrow. And today's friends can be tomorrow's enemies.

As the flattery of friends corrupts, so often do the taunts of enemies instruct.

Nothing is stable in the realm of power, and even closest of friends can be transformed into the worst of enemies.

Understand that some of your enemies are amongst your best friends.

Friend, my enemy, I call you out. You, you, you there with a bad thorn in your side. You there, my friend, with a winning air. Who pawned the lie on me when he looked brassly at my shyest secret. With my whole heart under your hammer. That though I loved him for his faults as much as for his good. My friend were an enemy upon stilts with his head in a cunning cloud. -Dylan Thomas

Friends can become enemies, and enemies can become friends. Ego and pride can turn what is good into bad, and kind words can turn what is bad into something good.

Make use of every friend — and every foe.

Treat your friend as if he might become an enemy.

It pays to know the enemy - not least because at some time you may have the opportunity to turn him into a friend.

Friends must always be treated as if one day they might be enemies.

Enemies strengthen you. Allies weaken.

And whom do I call my enemy? An enemy must be worthy of engagement. I turn in the direction of the sun and keep walking. It’s the heart that asks the question, not my furious mind. The heart is the smaller cousin of the sun. It sees and knows everything. It hears the gnashing even as it hears the blessing. The door to the mind should open only from the heart. An enemy who gets in risks the danger of becoming a friend.

It takes your enemy and your friend, working together, to hurt you to the heart: the one to slander you and the other to get the news to you.

Because I had goodwill for all, / I thought all were my friends. / And then I learned of treachery, / that some preferred my end. / It wasn't the goodwill I felt / that made someone a friend. / What handy day, the one I learned / the meaning of the word. / How good to know my enemies /(though their reasons are absurd!)