In the days of Mordechai and Esther, the Jews went from being the target of annihilation, to being the heroes and victors. It was a miraculous 180-degree shift in fortune. Joy comes both from seeing justice served upon our enemies, as well as being raised from the pit ourselves. One who thought he was in danger and suddenly discovers he's safe, laughs aloud in relief. One who thought he lived alone in a hostile world and suddenly discovers that God is really there, laughs aloud in joy.
Human beings see the world from a finite perspective.
The reality, however, is that God and His universe is infinite. But since we are tied to the finite physical world by our bodies, we're forced to live within the illusion of the finite world. Drink is an opportunity to transcend limitations that blind us to seeing God more clearly. The message of Purim is that even though it's hard to see Him, God is here in the world. Even when things look bad, even if we're suffering, in some way it has got to be all for the best, because there's a beneficent God behind everything, manipulating events for our good.