As a retired firefighter and combat veteran, I’ve been in some pretty tough situations. But the hardest thing I’ve ever done was sit my four children down and tell them I had stage IV lung cancer.

Two weeks earlier, they’d watched me lay one of my co-workers to rest after he’d died of stage IV pancreatic cancer. He was only 33. He was also a close family friend, so they had a front-row seat to his decline. They were worried I was...