Here’s an interesting quote by Charles Haanel:
“The “I” of you is not the physical body; that is simply an instrument which the “I” uses to carry out its purposes; the “I” cannot be the Mind, for the mind is simply another instrument which the “I” uses with which to think, reason, and plan.
The “I” must be something which controls and directs both the body and the mind; something which determines what they shall do and how they shall act. When you come into a realization of the true nature of this “I”, you will enjoy a sense of power which you have never before known.
Your personality is made up of countless individual characteristics, peculiarities, habits, and traits of character; these are the result of your former method of thinking, but they have nothing to do with the real “I.”
When you say “I think” the “I” tells the mind what it shall think; when you say “I go” the “I” tells the physical body where it shall go; the real nature of this “I” is spiritual, and is the source of the real power which comes to men and women when they come into a realization of their true nature.
The greatest and most marvelous power which this “I” has been given is the power to think, but few people know how to think constructively, or correctly, consequently they achieve only indifferent results. Most people allow their thoughts to dwell on selfish purposes, the inevitable result of an infantile mind. When a mind becomes mature, it understands that the germ of defeat is in every selfish thought.”