"Forgive us our trespasses" is a part of the cry of our souls twice a day as we utter the words of the Our Father and pray the Prayer of Confession. This is an acknowledgement of a number of things. Here are two:

This is a world of ache. Eden is gone and I think we are born expecting it to be here. This Eden-less space, according to the psalmist, is a land where there is no water. We are thirsty and what we long for is not here. Yes, it is in God, but when hunger/thirst strike us, faith isn't our natural default. We seek other gods by looking to other things (sometimes things forbidden) to assuage the deep ache within. In simple ways our hearts wander and we look for life outside the camp of God. We own this when we say, "we have not loved you with our whole heart."
It is an acknowledgment that we are still broken and still "being saved" (1 Cor 1:18). Though we find our life in Christ and feel buoyed up in our spirits by interactions with him, in unguarded moments when we feel lonely, bored, threatened, afraid, hungry, tired, etc., we easily default to behaviors that are less than holy--we ALL have familiar sins that "so easily beset us." We shouldn't be surprised when these appear--only sad that we did not see them coming in time to ask for help to face them. Whenever I fail, I always say (echoing Brother Lawrence), "This is the best I can do, Father. And if you do not help me, things will only get worse from here."

We can grow and not keep losing ground in deeper and deeper sin, but we will never be all that good at faith this side of eternity--at best we carry the acumen of a child. We will fail in our love of God and our love of the other. But that is not the end of the world. He remembers that we are dust (Ps. 103). And, the truth is, he is looking for our faith, not our perfection (it is faith that pleases him - Heb. 11:6). Hence, he offers us gratuitous forgiveness. He is more faithful to forgive us our sins than we are faithful to sin (1 Jn. 1:9). We receive that when as we pray these Offices each day and as we sit before a priest and share our brokenness In the sacrament of reconciliation (a sacrament that is pretty pale to us Protestants).

Be ok with not being perfect, but run like the wind to God when you notice you are not. And mean it when you say to him, "Lord, you lead me not into temptation...you deliver me from evil." What we are saying is, "Lord, help me discern the ache and hunger building in me so that my struggle can be had as I say NO to the impulse of my flesh by embracing the grace to defeat temptation and NOT just when I am defeated by sin and enter the struggle embracing grace to overcome the guilt and bruising caused by sin. I would rather seize the grace that prevents versus the grace that restores, but either way...THANK YOU FOR GRACE! Amen!"