I think it is the ultimate humility to acknowledge that despite our best efforts, we probably will sin. It is a hallmark of human psychology that the more modest the goal, the more achievable it is.
Perhaps it means lessening of sins, as Daas Yochid said.
I once heard that one of the Vishnitzer Rebbes said that this refers to the Aveiros that happen when you come to your Rebbe. You can’t go back three bite-size steps for Osseh Shalom, you can’t Daven Shmone Esrei as you normally would because at one point you get knocked over, you can’t Bentch sitting down, you might not have a Kezayis in place you Bentch.