Ideas in this post were taken from class discussion, Honors 202
We Catholics have this concept of there being levels of sin. Some (which we call venial) only damage your relationship with God; others (mortal) destroy that relationship. (Though not beyond repair.)
Yet, as Anselm says in Cur Deus Homo, to take even the slightest glance which is contrary to God's will is an unspeakably grave sin.
An analogy I came up with is that of deleting files on your computer. You delete something once and it goes to the recycle bin. You delete it from the recycle bin and it's a lot harder to find, but my dad the Computer Genius of the World says that it still exists somewhere on your hard drive. Even after deleting it twice it's still not totally gone.
Sin is like that. You delete God from your life again and again and again and that relationship is still not gone forever. As one of my classmates said, redemption is God's version of the restore point.