Nothing is quite honest that is not commercial. Robert Frost

Forgive me my nonsense as I also forgive the nonsense of those who think they talk sense. All I insist on is that nothing is quite honest that is not commercial. You must take that as said in character. Of course I don't mean by that that it isn't true. Nothing is true except as a man or men adhere to it — to live for it, to spend themselves on it, or to die for it. Not to argue for it! There's no greater mistake than to look on fighting as a form of argument. To fight is to leave words and act as if you believed — to act as if you believed. Sometimes I have my doubts of words altogether and I ask myself what is the place of them. They are worse than nothing unless they do something, unless they amount to deeds as in ultimatums an war crys. They must be flat and final like the showdown in poker from which there is no appeal. My definition of literature would be just this, words that have become deeds.

Remember all I say is said in character. I urge nothing.

From Letters of Robert Frost, Volume I: 1886 - 1920 (US link).