The sniper is the one military role that video games might actually adequately prepare us for. It's mostly lying down far away from the fight, lining bad-guy faces up with the scope and using some simple hand/eye coordination to blow them away. Even super realistic movies like The Hurt Locker don't make it look all that different from playing a game of Callfield: Battleduty.
"Hell, this 'Iraq' bullshit looks easy."
Actual sniping is less about lining up the cross hairs and more about having a complex understanding of physics. It's one thing to shoot a guy standing 20, 50 or 100 feet away. It's another thing entirely to make that shot from 1.5 miles away, as Canadian sniper Rob Furlong did.
At that distance, you have to take wind resistance into account, because it's going to slow your bullet down. And you also have to keep in mind that your bullet will drop while it's in flight. Furlong's shot may have taken up to four seconds to hit, and dropped 256 feet on its way to hitting that terrorist. This means that he had to aim several hundred feet above the head of his target to make that shot. Wind resistance and drop aren't the only things to keep in mind, either. Gunpowder burns at a higher rate when it's cold and a lower rate when it's warm, which causes bullets to hit high in warm weather and low in cold weather. And while you're checking on the weather, make sure to pay attention to the elevation -- the thin air at higher altitudes makes your bullets fly faster and flatter.