Australian psychologist Alan Richardson took 3 groups of basketball players and tested their ability to take freethrows. Then he instructed the first group to spend 20 minutes a day practicing freethrows. He told the second group not to practice and had the third group spend 20 minutes a day imaging that they were shooting perfect baskets.
 
As might be expected, the group that did nothing, didn't improve, the frist group improved by 24 % but through the power of imagery alone, the third group improved an astonishing 23 %, almost as much as the group that practiced physically.
 
Mary Orser and Richard Zarro, Changing your Destiny (New York Haper & Row, 1989, p. 274