[Editor's note: The staff of Parade is sad to announce that Lt. Col. Mark M. Weber died Thursday, June 13, at his home in St. Paul, Minnesota. He was 44. For more about his incredible life story, see his obituary in the Minneapolis StarTribune. We express our deepest condolences to the Weber family.]

After a routine physical revealed that Lt. Col. Mark M. Weber had stage IV cancer, the 41-year-old dad began writing a letter to his boys, Matthew, Noah, and Joshua. That letter became a book called Tell My Sons, filled with the advice he wouldn’t be able to share in person. In this excerpt, Weber recounts what he learned from his own dad.