Several years ago I was photographing in Yellowstone National Park rather early in the morning as I recall it was looking East down the Nez Perce Creek. Everything about the lighting with mist and all was perfect. Just after removing my camera from the tripod and placing it back in my backpack from behind my view a flock of ducks or geese in perfect "V" formation flew into the scene in just the right position of what would have been the frame. Oh well, that's how it goes at least the picture remains in my mind's eye (the location of my best pictures that got away).