A Warning Against Unwise Cursing Lest The Fact Reach The One Who Is Cursed (Ecclesiastes 10:20).
‘Do not curse the king, no, not in your thought. And do not curse the rich, even in your bedroom. For a bird of the air will carry the voice, and that which has wings will carry the matter.'
We are wise always to watch what we say or think, for there are always those who are willing to carry what we say to those we speak against. So the wise man curbs his tongue and is careful what he says, especially in public, but even in private. He does not speak one way in private and another way in public. He only says what he would not mind others hearing, for who knows who will spread the tale?.
The idea is based on the fact that kings and important people used to plant spies so that they knew what people were saying. But we know that God knows all that we say and are therefore to be even more careful.