In any art, you don't know in advance what you want to say - it's revealed to you as you say it. That's the difference between art and illustration.
To me documentary photography means making a picture so that the viewer doesn’t think about the man who made the picture. At its esthetic core is very old tradition in art: naturalism. And its purpose is to document all facets of social relationships.
We look at the world and see what we have learned to believe is there. We have been conditioned to expect... but, as photographers, we must learn to relax our beliefs.