The most pervasive theme in Maurice Maeterlinck's The Blue Bird is that happiness is achievable but must be actively pursued. The children set out on a quest to find the elusive Blue Bird of Happiness, but they encounter obstacles, danger, and fear along the way. Mytyl comes to symbolize the human fears that grip everyone during the pursuit of happiness. She lacks courage and is ready to turn back and give up on the quest numerous times. However, in the end, both she and Tyltyl realize that happiness, symbolized by the blue bird, has been in their home all along; they simply have not recognized and valued it.

The children visit the Palace of Happiness, and it is there that many luxuries of life are personified. The luxuries symbolize those ideals enjoyed by few in an ironic display of happiness: The Luxury of Being Rich, The Luxury of Satisfied Vanity, The Luxury of Drinking when you are not Thirsty, The Luxury of Eating when you are not Hungry, The Luxury of Knowing Nothing, The Luxury of Understanding Nothing, etc. Such luxuries are personified as ugly and disfigured. The Luxury of Understanding Nothing is blind. The Luxury of Sleeping More than Necessary has hands made of bread crumbs and eyes made of peach jelly. The Luxury of Eating has legs made of macaroni. Light, symbolizing knowledge, warns the children:

They are very affable. . . . They will probably invite you to dinner. . . . Do not accept, do not accept anything, lest you should forget your mission.

This is a cautionary statement meant to remind readers that it is easy to fall into the luxuries of life, but those ideals are self-serving and will not lead to ultimate fulfillment.

The Palace of Night shows a conflicting image of mankind. Here, it is clear that mankind is making some progress, weakening some of the hardships of the world. When Tyltyl asks if he should be careful when examining sickness, Night responds:

They are very quiet, the poor little things. . . . They are not happy. . . . Man, for some time, has been waging such a determined war upon them! . . . Especially since the discovery of the microbes. . . . Open, you will see.

Outside the plot, the reader can understand how this is not a situation of gravity. Indeed, this is something to celebrate. However, Night justifiably is concerned about opening the door of War:

They are more terrible and powerful than ever. . . . Heaven knows what would happen if one of them escaped! . . . Fortunately, they are rather heavy and slow-moving. . . . But we must stand ready to push back the door, all of us together, while you take a rapid glance into the cavern.

And, indeed, it does take the efforts of the entire group to close this door. Thus, humanity is both making progress in treating illness and in escalating the violence of war.

The power of family is reinforced throughout the play. The brother and sister experience this magical, dreamlike world together. If it is just a dream, it is a shared dream, one they both recall upon awakening. The power of a mother's love is personified, and the children examine how much more beautiful it makes their mother as she tells them,

Do you understand, Tyltyl dear? . . . You believe yourself in Heaven; but Heaven is wherever you and I kiss each other. . . . There are not two mothers; and you have no other. . . . Every child...