Though sin often brings immediate pleasure, it gives no lasting joy.
As soon as a baby enters the world, the baby is immediately introduced to pain. It is somewhat symbolic that life begins with a cry.
The Advent season is that time when we seek to, in a manner of speaking, mute our memory of what has already happened, that we might brighten our joy that it happened. We leave the already of His advent to taste the bitter of the not yet. We, in short, go back, that we might look forward to His coming.