The subconscious mind does not recognize negation. When engaged in activities that make us nervous, we oftentimes will rally ourselves by identifying our feared outcome and working against it. For example, someone playing golf might think, "Okay, don't miss the ball. Don't miss the ball."
What the subconscious mind hears: "Miss the ball."
So, if you want to encourage yourself to succeed, you have to always think of it in positive terms. This, I guess, is the power of positive thinking. Don't think,"Don't miss the ball." Think, "Hit the ball!"