Check out the videos. There's one on youtube of a female journalist who'd never fired a gun in her life, getting a head shot on a silhouette target at 750 yards, on her very first shot...ever!
I think the difficulty of the decision was mostly fabricated in Hollywood to contribute to the plot, but it would be interesting to read the book to discover when, or if, the decision caused so much emotional turmoil at the time. My guess is that it did not, but only later may have caused some regret.