Taken from Dom Scupoli's The Spiritual Combat.
HOW TO DISCOVER WHETHER WE DISTRUST OURSELVES AND PLACE OUR CONFIDENCE IN GOD
The presumptuous man is convinced that he has acquired a distrust of himself and confidence in God, but his mistake is never more apparent than when some fault is committed. For, if he yields to anger and despairs of advancing in the way of virtue, it is evident that he has placed his confidence in himself and not in God. The greater the anxiety and despondence, the greater is the certainty of his guilt.
The man who has a deep distrust of himself and places great confidence in God is not at all surprised if he commits a fault. He does not abandon himself to confused despair; he correctly attributes what has happened to his own weakness and lack of confidence in God. Thus he learns to distrust himself more, and he places all his hopes in the assistance of the Almighty. He detests beyond all things the sin into which he has fallen; he condemns the passion or criminal habit that occasioned his fall; he conceives a deep sorrow for his offense against God. But his sorrow, accompanied by peace of mind, does not interrupt the method he has laid down, nor does it prevent the pursuit of his enemies to their final destruction.
I sincerely wish that what has been proposed here would be attentively considered by many who think they are very devout. yet from the moment they commit a fault they will not be pacified, but hurry away to their director, more to rid themselves of the distress arising from self-love than from any other motive. Their principal care should be to wash away the guilt of sin in the Sacrament of Penance and to fortify themselves with the Eucharist against a relapse.