How important is it to practice mentally? If you are physically talented or you have the knowledge to execute on the job or if you think your parenting skills or your mechanical skills as an athlete are good, then why should you engage in mental practice?
The answer is compelling: match two people with equal physical talents in a competitive encounter and the person who performs stronger mentally will win most of the time.
Mental practice is an extremely valuable tool. It is used for two primary purposes. First, it enables you to view your competencies, to motivate you in executing, and that's the way it is commonly used. Mental practice is also useful as a learning tool. With this tool, you actually can learn a skill or you can learn sales techniques or many other things Basically, if you can see what you want to do in your mind, then you can execute it mentally practicing until you "package" the skill.
From "Coming In First" by Dr. Jack H. Llewellyn