The Mastermind Power Principle by Napoleon Hill

Having clearly defined your goals and purposes in thought and in writing, it is advisable to select an individual or individuals with whom you can share your plan for achievement. The mastermind principle is defined as an alliance of two or more people, working together in a spirit of perfect harmony to accomplish a definite purpose. The value of the “gathering together of those of like mind” is self-evident. Harmony in a home results when a man and woman work toward the establishment of a relationship that is mutually satisfying and productive of comfort and happiness for both.
Your mutual agreement with your employer to work toward high sales is a form of masterminding. If your major purpose in life is an ambitious one that extends beyond the accumulation of the ordinary requirements of subsistence, you will probably need the help of others in achieving it.
The mastermind principle is a means by which you may use the experience, the education, the talent, the influence, and perhaps the finances of other people to aid you in carrying out your major purpose. Your mastermind alliance may begin with your association with one other person. The number of alliances you will require directly depends entirely on the nature and the extent of the purposes of your alliance. A “meeting of the minds” must be regular, must be mutually beneficial, and must always be harmonious in the basic matters of sincerity and trust.
Source: Succeed and Grow Rich Through Persuasion. The Napoleon Hill Foundation. Penguin Books. 1991. Pgs. Pgs. 79-80.