TO WASTE ONE'S BREATH
Well, what does it mean to waste one's breath? The simplest definition that comes to mind is to talk a lot and in vain... In Polish we also say 'mówić jak do ściany', which is actually a nice thing as in English we can also use exactly the same phrase, i.e. to talk to the wall.
My personal experience:
Frankly speaking, I don't like talkative people. Most people today prefer talking rather than listening to others, which really frustrates me sometimes. There are many situations in which other people's ideas, opinions, etc. can never be uttered because others take control of the 'dialogue space'.
My question to you:
Do you like people who talk a lot? Do you ever have problems voicing your opinion? Why?