They are generally very dependable. If you hit something really hard, they can fly out. You can usually just push them right back in and you're good to go. (just make sure you inspect very carefully for small cracks around the end). I have seen them come out if the serving fit is way too tight also. Some brands fit into the arrow tighter than others. People often use plastic wrap or a plastic baggy as a "shim" to tighten them and it does work. I have never done it, but you will often read to not ever glue the push-in nocks to the arrow. Dry firing is not really a concern because even if it comes out it will still push the arrow in front of it.