"Photography is about finding out what can happen in the frame. When you put four edges around some facts, you can change those facts." - Gary Winogrand.
-What does this quote mean?

This quote to me means that there are facts and yet those facts can be changed through photography. In photography, the truth is set in the photo. When you take a picture of a certain subject you are making that photo the truth. It is what you see and capture that is real and truly what is to be seen. But, with the slightest change in the photo or point of view in the picture that is changed may even completely change the facts of the photo and the truth behind the photo.