The main purpose of the groin kick are to:
- Cross in the distance (kicking range ->punching range).
- Force your opponent to drop his arm (expose his head), or raise his knee (stand on 1 leg).
- Put your opponent in defense mode (He can't attack you at that moment).
- ...
It's a good "door opening" move. You can use it to create many other opportunities. So the groin kick can be the root of a tree. You can develop a full growing tree from it.
If you have repeat the groain kick over 1,000,000 times, you can do it without thinking. Your experience in that area will be more than your opponent has. That will be your advantage.
IMO, the secret technique is a technique that you have used over 1,000,000 times on different opponents.