The most important principle in persuasive communication is what I call outside-in thinking: the ability to plan your approach and frame your message according to a deep understanding of how the other person thinks and how they view the situation. Outside-in communicators know that one size does not fit all; it all starts with taking the perspective of the other person.
Throughout history, great generals have applied this concept by getting into the mind of their adversaries and adjust their strategy accordingly. Although “adversary” isn’t the way we want to consider those we’re trying to persuade, the principle of outside-in thinking is the same in both contexts. A story I just read about U.S. Grant in The Man Who Saved the Union, by H.W. Brands, illustrates this idea beautifully.
In February 1862, Grant commanded the Union forces that attacked the neighboring Confederate forts, Henry and Donelson, which guarded the Tennessee and Cumberland Rivers. Fort Henry fell relatively quickly, but Fort Donelson was a tougher nut to crack. It was nominally commanded by John Floyd, but Grant knew that he would defer to the judgment of his second in command, General Gideon Pillow. As Grant later wrote in his memoirs, he knew Pillow from their previous service together in the war against Mexico, and he was confident that he could approach aggressively against him.
Knowing they could not hold out for long, on February 15th the Confederates launched a vigorous attack against the Union forces in attempt to escape the fort. The plan came close to success, but the Union lines just managed to hold on. Fearing Union reprisals, both Floyd and Pillow—establishing a tradition that incompetent CEOs follow to this day—snuck out during the night, leaving Simon Bolivar Buckner to unconditionally surrender the fort.
Buckner, who had served with Grant in California, told him that if he had been in command Grant would not have gotten up close to Donelson as easily as he did. As Grant later said in his memoirs: “I told him that if he had been in command I should not have tried in the way I did.”
 He was pretty ticked off about the unconditional surrender demand, having banked on his long friendship with Grant and the fact that he had loaned him money to return home from California after he left the service.