WereNotInvincibleGod has a way of showing us we’re not invincible; that’s one thing I’ve learned this year.

This week I celebrate my 75th birthday. Last year, I climbed Mt. Kilimanjaro, Africa’s tallest peak, where African friends call me Babu Simba—Grandfather Lion. I came in second place in a downhill alpine ski race. I bicycled 500 miles across Oklahoma in Oklahoma FreeWheel. I parachuted out of WWII-vintage airplanes as a member of the WWII Airborne Demonstration Team. I backpacked Idaho’s Sawtooth Mountains with my grandson Skylar and old friend Dan Case. . .

Over the years I’ve been a cop, a college professor, the best-selling author of over 60 books. I was a U.S. Navy journalist, a U.S. Army Special Forces soldier (the Green Berets). I’ve climbed mountains, kayaked the Inside Passage to Alaska, canoed the Yukon Territory, rode horses across Alaska, been a professional rodeo bronc rider and rodeo clown-bullfighter. I’ve gone to war several times, ran with the bulls in Spain, served as a combat correspondent for publications such as Time-Life, Soldier of Fortune, and Tulsa Tribune, and turned pro as a kickboxer at age 51. I raced a mountain bicycle down the top of the Rocky Mountains, dived for pirate treasure, set a world’s cross-country flight record in an ultralite aircraft, was a finalist for NASA’s “Journalist in Space Project,” solo sailed the Caribbean, hopped freight trains. . .

I explain for a purpose. Even as I aged, I felt myself invincible and that I would always climb mountains, sail seas, and backpack wildernesses. . . Then, I contacted prostate cancer that necessitated surgery. I suffered weeks of excruciating pain, followed by much-reduced strength and energy. Muscles sagged, I lost weight, and just like that I was an old man.

For the first time in my life I realized that I am completely mortal after all and that God was telling me that He had given me a life few people have known—but that one day it would be over. Thank you, God.

On January 18, History Channel will premier its mini-series called SIX (about the counterterrorist activities of SEAL TEAM SIX. “What if one of your own were taken? What would you do to get him back?”) Accompanying the series will be my two-volume novelization of the series entitled SIX: BLOOD BROTHERS; and SIX: END GAME.