A woman, when she is in labour, hath sorrow, because her hour is come; but when she hath brought forth the child, she remembereth no more the anguish, for joy that a man is born into the world. (John 16:21)
During Advent, I and many of my brothers and sisters in Christ, will be giving something up. This is a tradition that goes back a long ways. I'm not sure how far back,. but the Church has a tradition of fasting before feasting. It is an allegory of the world. We suffer now, only to behold Christ our King later.
Israel fasted and prayed and underwent much tribulation as they waited for the Messiah. Mary and Joseph journeyed to Bethlehem as they anticipated Jesus' birth. And Jesus says to us in Luke 5:33-35,
"And they said to him: Why do the disciples of John fast often, and make prayers, and the disciples of the Pharisees in like manner; but thine eat and drink? [Luke 5:33] To whom he said: Can you make the children of the bridegroom fast, whilst the bridegroom is with them? But the days will come, when the bridegroom shall be taken away from them, then shall they fast in those days."
We are remembering the time before Christ, and we are anticipating his second Coming, so now we fast, preparing our souls for heaven. We fast to strengthen our spirits and teach them that we do not need things like coffee (what I'm giving up), but we need Christ.
The fasting can be from anything we enjoy. We can abstain from tv, or candy, anything really. Just to remind ourselves, it is not yet the time for rejoicing, but the time for preparations.