"The great significance of this work lies in its presentation of a particular moment. If [an artwork] is to convey to the viewer a sense of real movement, it has to portray a fleeting moment. We must be convinced that no part of the whole was in its present position just prior to this instant, and that no part will be in the same position just afterwards. If this is so, the [artwork] will forever be a living image to countless millions."  
-Goethe, Essays on Art & Literature (Italics added for emphasis)


A good photograph is a living image of a fleeting moment.