Here’s an interesting quote by William Walker Atkinson:

“The trained occultist will concentrate upon a subject or object with a wonderful intensity, seemingly completely absorbed in the subject or object before him, and oblivious to all else in the world. And yet, the task accomplished, or the given time expired, he will detach his mind from the object and will be perfectly fresh, watchful and wide-awake to the next matter before him.

There is every difference in being controlled by involuntary attention, which is a species of self-hypnotization, and the control of the attention, which is an evidence of mastery.

The secret of Mental Concentration lies in the control of the Attention. And the control of the Attention lies in the exercise of the Will.

All of the occult authorities begin teaching their pupils Attention as the first step toward Mental Concentration. They instruct the pupil to examine some familiar object, and endeavor to see as many details as possible in the object. Then after hearing the pupil’s report, the master sends him back to the task, bidding him seek for new details, and so on until at last the pupil has discovered about all concerning the object that can be discovered. The next day a new object is given him, and the process is repeated. First simple objects are given, and then more complex ones, until at last objects of great complexity are easily mastered. In this way not only is the power of close observation highly developed, but the faculty of Attention becomes so highly strengthened that the pupil is able to exert the greatest amount of Mental Concentration with scarcely the consciousness of effort. And such a person then becomes a very giant in the manifestation of Mental Influence. For he is able to hold his mind “one-pointed,” as the Orientals describe it, until he has focused and directed a mighty degree of Mental Influence toward the desired object.”