When shooting flushing birds, you can’t use shooting sticks and you can’t take a little extra time and aim. The target is always moving at an unknown speed and most of the time an unknown distance. In the instance of a flushing bird, after you are startled by the flushing of the bird, the bird is trying to get away from you as quickly as it can. It will be flying on a sometimes varying angle, darting and changing directions as many as two or three times at the beginning of their flight!
You must be able to react with the gun, mount the gun to the bird and merge the muzzles onto the line of the bird from underneath, all the while not knowing where the bird is going!
So, as you can see, you must be able to react to whatever the bird does, all the while looking at the bird and not looking at the gun to see where it is pointed. Because if you look at the gun, then your eyes have come off the bird.
And how do you know where the bird is, much less where it is going to be? You must learn through practice how to move and mount the gun and how to know where the gun is pointed without looking at the gun. And you need to know what this all looks like before you go to the field and go hunting.