My neighbor upstairs has a poster of this photo hanging in the front entrance of our apartment building, and I see this wonderful photograph every day! Nice to read a little bit of the history behind it.
The story linked to in CGW's post makes that fairly clear (once you get past the ads).
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2