There is no secret that to get good at something you need to practice it, and a lot! Martial Arts is no different, whether it is Kickboxing or Jiu Jitsu you need to put in the time to reap the rewards.
In order to be able to pull of a move or technique under a high stress situation you would of had to have drilled it hundreds if not thousands of times. When your brain wants your body to perform an action it sends a stimulus down a path of nerves to a group of muscles.
The stimulus then tells your muscles what to do. As you send the same stimulus down the same nerve path it starts to get there faster and faster every time. So the more you practice a move the faster your brain will be able to tell your body what to do.
And this creates muscle memory, so next time your coaches keep you practicing a fundamental movement over and over, now you know why.