Quail are tricky to shoot for a variety of reasons. They can jump from anywhere, and as they are often up high the dogs will not always flush them. There have been plenty of times where I have positioned another hunter where I expect them to get a shot, and end up getting the shot myself because the bird breaks in an unpredictable direction.
Quail dip and dive around, behind and below cover, so there is often not much time to get a shot away, or to have a second shot.
All this means that to successfully shoot quail you need to be very, very fast on the shot. Split seconds matter, so concentration and positioning are important. Concentration is crucial, if you are not concentrating hard you will not get a shot because the quail will have got behind some structure before you get the gun up.
When the dog indicates it is on to quail it pays to concentrate hard and stop talking to your mate or look at your phone or do anything that is not totally focused on the dog and where it is working.
When the quail breaks it is crucial to react instantly, rather than think about the shot or lead or anything else. Get the gun up and pull the trigger. Or you will be too late on the shot.