St. John Climacus
“We ought to be on our guard, in case our conscience has stopped troubling us, not so much because of its being clear but because of its being immersed in sin. A proof of our having been delivered from our failings is the unceasing acknowledgement of our indebtedness. Nothing equals the mercy of God or surpasses it. To despair is therefore to inflict death on oneself. A sign of true repentance is the admission that all our troubles and more besides, whether visible or not, were richly deserved.”
Source: St. John Climacus, The Ladder of Divine Ascent