The following illustration from A Primer on Meditation points out what happens when the mind is directed and focused on one thing:

"M.A. Rosanoff, long associated with Thomas Edison, had worked futilely for over a year to soften the wax of phonograph cylinders by altering their chemical constitution. The results were negative. Rosanoff relates how he mused night after night trying to 'mentally cough up' every theoretical and practical solution. 'Then it came like a flash of lightning. I could not shut waxes out of my mind, even in my sleep. Suddenly, through headache and daze, I saw the solution. The first thing the next morning, I was at my desk; and half an hour later I had a record in the softened wax cylinder...This was the solution! I learned to think waxes...waxes...waxes, and the answer came without effort, although months of thought had gone into the mental mill.'"