Adding to my thoughts on the sin of Despair (see earlier post Life Is Unpredictable):

In The Lord of the Rings Tolkien contrasts Despair with various virtues. Sam, the true hero Tolkien later said, demonstrates Loyalty, and so helps save Middle Earth. Frodo demonstrates many virtues, including Duty, and so helps save Middle Earth. And so on. The heroes persevere, even when all looks hopeless, carried forward by loyalty, duty, honor, courage.

Two important figures illustrate the sin of Despair: Saruman and Denethor. Denethor, the Steward of Gondor, beheld the might of the enemy, and concluded that all would be lost. He killed himself and tried to kill his son. Saruman, the Wizard, also beheld the might of the enemy, and concluded that resistance was futile. He allied himself with the Enemy, Sauron. A shared characteristic of each of these characters is pride.

Despair is a form of pride, assuming we know infallibly that things are hopeless. Not a bad thing to remember in these days of terror amidst the War against militant Islam.