to promise the moon直译的意思是：向某人许诺月亮。其实这里的月亮和不切实际同义，即向（某人）作无法兑现的承诺；作出过度承诺。

【例句】
My husband promised me the moon when we got married: a big mansion, a flashy car and all the diamonds I could wear. But none of it happened!
我的丈夫在我们结婚时向我承诺：一座大豪宅、一辆华丽的汽车和所有我可以佩戴的钻石。但这一切都没有发生！

Greece is right to promise the moon, to gain the time to eliminate its primary deficit more smoothly.
希腊作出难以兑现的承诺，以便赢取时间更平稳地消除其基本赤字，这种做法没错。