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On Tuesday night, former Navy SEAL Eric Greitens won the nomination for governor of Missouri over the state’s attorney general, Chris Koster. Greitens, a Republican, will replace Democratic Gov. Jay Nixon, becoming Missouri’s 56th governor in January 2017.

Before entering politics, Greitens had a storied career as a Navy SEAL. He received a commission in the Navy in 2001, and then received orders to Basic Underwater Demolition/SEAL School. Greitens was there on Sept. 11, 2001, and his class would be one of the first to go through every phase of training with the understanding that they would soon be taking part in the Global War on Terror.

As a Navy SEAL, Greitens deployed to Afghanistan, the Horn of Africa, and Southeast Asia. In 2007, he deployed to Iraq where he served as the commander of an Al-Qaeda targeting cell. He currently serves in the Navy Reserves as a lieutenant commander.

Related: A Navy SEAL’s Advice On Living A More Fulfilling Life »

The weight of multiple deployments took its toll on Greitens. In 2015, he published “Resilience,” his fourth book, a compilation of letters between him and his Navy SEAL buddy struggling with alcoholism, job loss, and PTSD. In the book, Greitens explains his own struggle with severe mental-health issues in 2002 and how he eventually overcame them:

But for all of that, I don’t know that I’ve ever been knocked down as hard as the day I walked into that empty apartment and collapsed on the floor. I wouldn’t wish that on anyone. But in retrospect, I can see some good in it. It’s made me stronger and better in a dozen ways.

I’ve been fortunate in other ways as well. I’ve been able to learn from great examples of resilience: refugees who survived genocide, other Navy SEALs who endured the hardest military training in the world, wounded veterans who have rebuilt purposeful lives in the face of devastating wounds. The things I talk about in these letters are strategies I’ve used in my own life, strategies I’ve seen others use, and I know how much they can help.

We all need resilience to live a fulfilling life. With resilience, you’ll be more prepared to take on challenges, to develop your talents, skills, and abilities so that you can live with more purpose and more joy.

I hope something here can help you to become stronger. I look forward to walking with you on this path.

Greitens went on to found The Mission Continues in 2007, a nonprofit that seeks to help veterans transition from wartime service by serving in and leading their communities. His own personal resilience is what empowered him to get involved in politics as an outsider and go on to win the governorship.