Calmness of mind is one of the beautiful jewels of wisdom. It is the result of long and patient effort in self-control. Its presence is an indication of ripened experience, and of a more than ordinary knowledge of the laws and operations of thought.
A man becomes calm in the measure that he understands himself as a thought-evolved being, for such knowledge necessitates the understanding of others as the result of thought, and as he develops a right understanding, and sees more and more clearly the internal relations of things by the action of cause and effect, he ceases to fuss and fume and worry and grieve, and remains poised, steadfast, serene.
The calm man, having learned how to govern himself, knows how to adapt himself to others; and they, in turn, reverence his spiritual strength, and feel that they can learn from him and rely upon him. The more tranquil a man becomes, the greater is his success, his influence, his power for good.
-James Allen, As a Man Thinketh, Serenity