英语寓言故事-The Lion and the Eagle

AN EAGLE stayed his flight and entreated a Lion to make an
alliance with him to their mutual advantage.  The Lion replied,
"I have no objection, but you must excuse me for requiring you to
find surety for your good faith, for how can I trust anyone as a
friend who is able to fly away from his bargain whenever he
pleases?' 


Try before you trust.