"Chacun doit cultiver son jardin" is the final reflection of Candide, and this idea that one must cultivate his own garden--to paraphrase the metaphor: one must make one's own happiness--is the theme here that Voltaire wishes to convey. For, while Eldorado is "the best of possible worlds," it is not for Candide since he loves Cunnegonde; to Candide "heaven on earth" must include the object of his love or else his life has no meaning, thus proving the old adage of "one man's heaven is another man's hell."
In his satire, "Candide," Voltaire satirizes the pholosophy of optimism promulgated by Gottfried Wilhelm von Leibnitz, who held that God created the world, and since God is perfect, everything in the world is ultimately perfect. Candide's leaving the "perfect world" of Eldorado dispels Leibnitz's belief since he is not satisfied with this world. So, at the conclusion of Voltaire's satire, Candide states that each person must create his own happiness and find his own "best world":
Pangloss sometimes said to Candide, 'All events are interconnected in this best of all possible worlds, for if you hadn't been driven from a beautiful castle with hard kicks in the behind because of your love for Lady Cunegonde, if you hadn't.....and if you hadn't lost all your sheep from the land of Eldorado, you wouldn't be here eating candied citrons and pistachio nuts.'
'Well said,' replied Candide, 'but we must cultivate our own garden.'