vivid imagery produces a real stimulus
As said before, visualization and feel imagery is the language of the subconscious. Your self-image and physical body cannot tell the difference between what happens and what is vividly imagined.
Use vivid imagery when performing movements in your head.
Use vivid imagery when imagining the high pressure situations you eventually will be in.
Use this conscious language to speak to your unconscious, but when it's time to perform, let your unconscious come out.