Someone has said that courtesy is the cheapest, yet the most profitable, of all traits of a pleasing personality. This may be an exaggeration, but it is not an overstatement to say that courtesy is an essential trait of personality without which no one may become pleasing to his associates.
As to its price, we must admit that it is absolutely free. All it costs is: a positive mental attitude, sincerity of purpose, consideration for the rights and feelings of others, and a willingness to share your blessings with your fellowmen. Observe how all of these principles are interrelated so that the development of one leads to the achievement of others.
Courtesy is the habit of respecting other people’s rights and feelings under all circumstances; the habit of going out of your way to help a less fortunate person whenever possible; the habit of rendering useful service without the expectation of direct reward; and last, but not least, the habit of controlling selfishness, greed, envy and hatred.
Courtesy is a reflection of the spirit of fellowship without which no one may have dependable friends. It will often serve as an irresistible force with which one may disarm enemies and antagonists.
Source: PMA Science of Success. Educational Edition. The Napoleon Hill Foundation. 1961. Pg. 170.