The sender was Manning's famed sports trainer, Mackie Shilstone, who also helped tennis player Serena Williams and boxer Bernard Hopkins revive their careers.
That morning Shilstone had sent [Peyton Manning] passages from The Art of War, a [2,500] year old guide to battle written by the Chinese general Sun Tzu. Shilstone hoped the passages would inspire Manning, making him believe he had that one last game inside him.
Sun Tzu would be proud of Manning indeed.
No sports analyst worth his or her salt predicted Peyton Manning and his Denver Broncos team would win Super Bowl 50 -- especially not against the brash, nearly undefeated Cam Newton and his Carolina Panthers team. But win they did. Throughout the season Manning was dogged by calls for him to retire, that he was too old, his body falling apart. But whether or not those calls were correct, Manning and his team stood victorious when the confetti fell in San Francisco on the night of February 7, 2016.
Therefore, I'm so happy Sun Tzu likely had a hand in the success of a very special quarterback, thanks to the wisdom of a very special sports trainer.
If you're curious how else Sun Tzu, who lived 2,500 years ago, still influences the modern world, you can simply look at the current US Presidential race.