It's not just God's mercies that are "afresh each morning" (Lamentations 3:23), but our spirits are, too! He knows that our "meat suits" are temporary! He doesn't expect our flesh to withstand the inevitable death and decay of this world; that's why He's placed in each of us a spirit! Our spirit is the eternal part of our existence as human beings, the part that is able to draw closest to God.
When we decide not to let the hurt and failures of our past ruin our present, we aren't limited by anything!