Maugham's line takes place in an exchange between the titular characters. Princess September is distraught at her parrot dying. She is inconsolable, and the Maids of Honor, wishing to attend a party, quickly pack the Princess off in her room so that she can cry herself to sleep. The nightingale enters her room in the midst of her crying and without any prompting from the Princess sings an exquisite song. It is a transformative song, as it stops her crying and causes her to take notice. When she comes to and when the song has ended, she praises the nightingale in relaying how much she appreciated it. The nightingale expresses its gratitude and bows to the Princess, with Maugham adding the line that "Artists have naturally good manners and they like to be appreciated."
The line is significant because of its meaning. Maugham uses the line to express how the nightingale sees its craft and its gift. He sees it as something to bestow upon others. When it is freely appreciated, he reciprocates it with good manners. The nightingale likes to be appreciated, evidenced when she acknowledges his beautiful singing. Maugham establishes that the artist lives for their craft and sharing it with the world. The nightingale wishes to sing and share his gift with the world, in this case, the Princess. When the nightingale is appreciated in a free manner, he shows it with good manners. Maugham has a double meaning in the use of the sentence as it reflects his own desire to be appreciated. Maugham understood the value of being appreciated in his own time, reflecting how he himself "liked to be appreciated." Maugham recognized clearly the idea that the artist enjoys the sharing and reciprocation from his gift. It is a sentiment that the nightingale shares when it comes to the Princess. The meaning of the sentence is one where an artist is able to share their talent and receive due credit for it.
In order to understand the meaning of W. Somerset Maugham's line "Artists have naturally good manners and like to be appreciated," the reader must finish the allegory and perceive the nightingale's initial action as it relates to the rest of the narrative. Moreover, this line is embedded in the ideas of the artist W. Somerset Maugham himself, who observed,
The artist produces for the liberation of his soul. It is his nature to create as it is the nature of water to run down the hill.
From the narrative, then, the reader learns that "nothing gold can stay" as Robert Frost observed in one of his poems. That is, beauty/art cannot remain static; it must be created and re-created, renewed and reborn. After the princess obeys her narrow-minded sisters who tell her she should protect her bird by caging him, the nightingale, who begins to languish, tells her, "I cannot sing unless I'm free and if I cannot sing, I die." Princess September, who loves him and "appreciates" him, sets him free, although this action grieves her with its loss. However, in having acted so lovingly, she grows "extremely beautiful" in the years to come, having expanded her mind and soul beyond their selfish desires.
"Artists have naturally good manners" because they do not presume to know what is right for a person; further, artists "like to be appreciated"; they like to have others understand that they cannot be restrained in their creative processes--their freedom is essential.