The debt of the fellow servant is microscopic compared to what the first servant had been forgiven of. I attempted to do the math, and by comparison, this servant owed 1/600,000 of the amount owed by the first if taken literally, but the figures are intended to represent an infinite contrast. This is not to say the amount is insignificant, as a hundred denarii represented 100 days of work for an ordinary day laborer. This is no small sum. The contrast between the way the first servant is treated by the king and how this man is treating his fellow servant is meant to be outrageous! The servant does not reciprocate the forgiveness shown to him by the king.
The contrast is meant to elucidate the meaning of the parable. When we begin to understand the depth of our sin and the forgiveness offered to us by God, we in turn demonstrate the same kind of forgiveness to others in our life. Jesus here paints a picture of what imitation of the character of God is to look like. The only prerequisite is that we understand the depth of our own brokenness. In light of this, we begin to understand the depth of forgiveness offered to us in Christ Jesus. Praise be to God that He offers us opportunities to participate in His mission by offering the same kind of forgiveness in our relationship with others.