Enemy Unknown

Every time you feel that, all you have to do is to remember three simple truths:

First, is that YOU are chosen to be transferred into XCOM, because you are among the best warriors Earth could muster in its defense; you would not have been chosen if XCOM, if not Humanity, do not have any confidence that you have what it takes to succeed. 

Second, XCOM, as a whole, was created to be Mankind's first and last line of defense against the alien menace. To that end, the finest collection of this world's human talents and resources had been gathered to make us the most Vigilant, the most Reliable protectors of Humanity.

Third: X-COM is created because, at the end of the day, no one else in this universe will come to the rescue of Earth, and no one else on Earth itself comes even close in having a chance against the alien menace, except us. We have only ourselves, and each other, to depend on.

Look at how far we had gone, because of these three simple truths: How many times had the aliens be beaten back, had it not for our valor and will against impossible odds? And how would we be able to EVEN those odds, were it not for the intellect and resources at our disposal to turn the weapons of the enemy against them? How many innocents would had died in the aliens' terror attacks, their prayers unanswered, were it not for us coming to their rescue?