Satan drives many to despair when they discover that they do not have within themselves the strength (or even the desire) to fulfill God's will. A hurt that was so bad and damaging, for example, that they do not have the inner resources on their own to forgive; let alone to want to forgive. Yet they know they must forgive, and they cannot.
The key to defeating Satan when dealing with situations like this is to realize the devil WANTS your gaze to stay fixed on your own inadequacy or on God's immovable will, whereas God invites us to discover in HIM, in union with Him, the strength to do that which we are utterly incapable of on our own. This is St. Paul's great comfort: "My strength is made perfect in weakness." He comes to us even in our weakness. He unites Himself with us in all our helplessness. He stands with us. From Mary's womb to Calvary's tree, from Easter dawn to Ascension, from the descent of the Spirit to the glorious Appearing - He stands with us, and His gracious presence supplies us all that we lack in ourselves. He joins Himself to us in our Baptism and He does this for us continually in Absolution and in the Holy Eucharist. He teaches us to live from Him, to draw all strength from what He supplies. And because our doing of God's will is even at its best, always in great weakness, even when He is pouring in to us His strength, He graciously covers even the defects in our good works with His abundant forgiveness.
Rather than mustering the interior resources to do God's will, we confess we utterly lack them in ourselves and turn to the Blessed Trinity and ASK from Him what we do not have in ourselves, and which it is His delight to bestow on us. That is how we learn to live more and more from Christ - always receiving what He would give. Then we can say with Paul that though "I know that no good thing dwells in me, that is in my flesh" nevertheless "I can do all things through Him who strengthens me."
This utterly defeats Satan's trick. Self: remember this.