Visualization research has shown that there is a strong scientific basis for how and why visualization works.
We stimulate the same brain regions when we visualize an action as when we actually perform that same action. For example, when you visualize lifting your left leg, it stimulates the same part of the brain that is activated when you actually lift your left leg. This shared area of brain activation when we imagine an action and perform it has been demonstrated extensively in the scientific literature. A striking example of how visualization increases brain activation is seen in stroke.
When a person has a stroke (which is due to a blood clot in a brain artery), blood cannot reach the tissue with oxygen and nutrients, and that tissue dies. Tissue death then spreads to the surrounding area because it does not receive the blood supply anymore. However, if a person with this stroke imagines moving the affected arm or leg, brain blood flow to the affected area increases and the surrounding brain tissue is saved. Imagining moving a limb, even after it has been paralyzed after a stroke, increases brain blood flow enough to diminish the amount of tissue death. This is a very clear indicator of the power of visualization.
Athletes have been using hypnosis and visualization for a long time.
Studies have shown that athletes first imagine running the race in the goal time in as much detail as possible and are then able to execute it after practicing visualizing this. One study showed that "...visualizations under hypnosis enabled nationally ranked Stanford male gymnasts to execute for the first time several complex tricks that they had been working on for over a year. The gymnasts were able to eliminate timing errors in the tricks, to increase flexibility, and, possibly, to concentrate strength..." Another study showed that youth soccer players increased their confidence in playing when they visualized their moves. Visualization has also been shown to improve high jumpers clearing the bar.
"...visualizations under hypnosis enabled nationally ranked Stanford male gymnasts to execute for the first time several complex tricks that they had been working on for over a year..." Hypnosis works because it helps in decreasing anxiety and increasing focus.
"...youth soccer players increased their confidence in playing when they visualized their moves..." Visualization of your goals helps to increase your confidence.