白费口舌

白费口舌:

Literally means:

waste one's' breath; speak to the wind.

Actually means:

白费 means doing something, but in vain. 口舌 means words. This phrase means one speaks a lot, but to no avail.

It is often used in the cases of stating one's reasons, asking for help, offering suggestions, etc.

白费，没有效果；口舌，话语。白费口舌,指说了很多话但是不起作用，没有效果。

多用在说明理由，或请求帮助，或提出建议、劝告，等等。