Koudelka is a great example of how difficult it is to generalize about this (which I'm guilty of). Granted, there are many photos in the Prague 68 series that now transcend their context.
That said, this photo absolutely doesn't. It only makes sense within its context. It's all about context. You can only feel the tension because you know that in a few seconds Russian tanks are going to start rolling at the end of that street (actually in an hour, Koudelka got the hour of their arrival wrong). As opposed to the Cartier-Bresson photographs we've been discussing (like the one I posted above), this is not, from a compositional point of view, a great photo,
per se. You probably wouldn't stop and admire it were it be hanging on a museum wall. It begs context, it begs understanding. It's a very powerful photo but it becomes a powerful photo because of its context.
And also because Koudelka thought of taking that photo, had the instinct to take
that photo, a photo revealing the tension, anticipation of the moment just before. Takes a special kind of genius to do that. I certainly wouldn't have thought of it. I would have taken the photo with the tanks
in the street. And it wouldn't have been as good a photo.