Diminishing returns will have operated to the point where the marginal effect of outlays of every kind of commercial persuasion will have brought the average effect to zero.
Since this doesn't seem to make any sense, let me give the context in which it appears:
In a society where virtuosity in persuasion must keep pace with virtuosity in production, one is tempted to wonder whether the first can forever keep ahead of the second. For while production does not clearly contain within itself the seeds of its own disintegration, persuasion may. On some not distant day, the voice of each individual seller may well be lost in the collective roar of all together. Like injunctions to virtue and warnings of socialism, advertising will beat helplessly on ears that have been conditioned by previous assault to utter immunity. Diminishing returns will have operated to the point where the marginal effect of outlays of every kind of commercial persuasion will have brought the average effect to zero. It will be worth no one's while to speak, for since all speak none can hear. Silence, interrupted perhaps by brief, demonical outbursts of salesmanship will ensue.
Well, that's from J.K. Galbraith's The Affluent Society (1958 paperback edition).
I'm not good at responding to blog memes, but this one -- sent along by Blue -- was simple to do. Given how I normally react to memes, it's only natural that this branch of the meme stops here.