In his memoir The Summing Up, he explains the need for writers to "cut, cut, cut" their work:
"To do so now is more than ever necessary, for audiences are at once quicker-witted and more impatient than ever before in the history of theatre... Audiences in the past seem to have been willing to sit out scenes that were elaborately developed and to listen to speeches in which the characters fully explained themselves. It is very different now, and the difference has been occasioned, I suppose, by the advent of the cinema. Today, audiences... catch the gist of a scene in a few words and having caught it, their attention quickly wanders."
This was published in 1938. Isn't it amazing...he could be describing the shift from traditional broadcast and print media to the Web.