Webster’s New World Dictionary defines resilience as “bouncing or springing back into shape, position, etc. after being stretched, bent, or, esp., compressed or … recovering strength, spirits, good humor, etc. quickly; buoyant.”

That’s a dry, utilitarian and rather unimaginative but serviceable definition.

Eric Greitens, a St. Louisan who is a  former Navy SEAL and founder of the Mission Continues here, has written a book of essays in letter form explaining and praising the many ways one can find and use resilience to push on through and overcome many of life’s obstacles. 

Greitens speaks from experience. As he states early in the book, his first marriage fell apart late in 2002, and he faced one of the formative crises in his life.

“I came home to an empty house,” he writes in an early letter to the SEAL buddy he calls Zach Walker. “Thank God for work. I’d get out of bed, get a uniform on and get in on time. When I came home, I’d often fall straight into bed, and for the life of me, I couldn’t get out of it until the next morning.

“Trash piled up in the kitchen. The dishes went unwashed. I never seriously thought of killing myself, but I was so ashamed. When I look back on that year of my life … there’s almost nothing there.”

What matters here, Greitens writes over and over in different ways and using different examples, is how one reacts to such a challenge to one’s existential being.

“Pain can break us or make us wiser,” he writes. “Suffering can destroy us or make us stronger. Fear can cripple us, or it can make us more courageous.

“It is resilience that makes the difference.”

Another way to put this point is that what counts isn’t so much the challenge one faces, but how one reacts. 

In his work with the Mission Continues, Greitens has set up a nonprofit organization in which veterans help other veterans to react to their recent history in the Iraq and Afghanistan war zones in ways that are positive for their future.

The Mission Continues helps post-/11 veterans find their way to education, service to others and productive lives after their time in uniform. This is a most challenging transformation that has laid low many a veteran who cannot make the adjustment from the adrenaline-producing stress of combat zones to what many vets discover is the boredom and banality of civilian life. 

So perhaps it’s natural that Greitens would shape his book as a series of letters to a fellow SEAL who’s struggling to get his life on track after serving in combat. 

A Rhodes scholar and author of three other books, Greitens is known on the national stage for his SEAL experience —  especially after a team of the elite Navy unit killed Osama bin Laden – and his TV appearances on “The Daily Show with Jon Stewart” and elsewhere. He’s also on the national speaker circuit, and won the $100,000 Charles Bronfman Prize in 2012 for his work as a leader in the Jewish community. 

Although his office immediately south of downtown St. Louis had pictures of the late John and Robert Kennedy on the walls, Greitens is exploring a run for Missouri’s governor next year as a Republican.

His book, written as a series of letters on various facets of resilience (Happiness, Models, Identity, Habits, Mastering Pain, even the virtues of observing Shabbat), is full of advice and stories in his distinctive voice: a bit high-toned with the occasional quote from a Greek philosopher or playwright thrown in.

It stretches credulity a bit to think that his former comrades in arms would take to Greek poetry and guidance, but Greitens is not the first person to point out that the trials endured by ancient Greek warriors are quite similar to those experienced by veterans today.

Jonathan Shay, who worked as a Veterans Administration psychiatrist in Boston, drew this parallel in two excellent books, “Achilles in Vietnam: Combat Trauma and the Undoing of Character” and “Odysseus in America: Combat Trauma and the Trials of Homecoming,” noting the similarity between the Trojan War and the Vietnam experience.

Greitens is updating some of these points by speaking more of contemporary issues facing veterans, and his advice can be broadly applied to civilians of all types who may have post-traumatic stress disorder (PTSD) or faced existential challenges in their lives.  He is mining the transcendent truths of how human beings survive and somehow, even, return to good humor and buoyancy, to borrow from Webster.

Here’s one example he uses. Adm. James B. Stockdale, who became H. Ross Perot’s vice presidential running mate in 1992, was a prisoner of war in North Vietnam for more than seven years. He eventually won the Medal of Honor for his leadership and steadfastness in the face of North Vietnamese torture and pressure to break.

Greitens reminds the reader of what he calls the Stockdale Paradox. In short, Stockdale never deluded himself about his situation; he never lied to himself.

Greitens quotes Stockdale: “You must never confuse faith that you will prevail in the end — which you can never afford to lose, — with the discipline to confront the most brutal facts of your current reality, whatever they might be.”

Stockdale had noticed that those POWs who tried to fool themselves about the seriousness of their situations were the ones who broke under pressure, perhaps to sign a confession of war crimes.

As it turned out, Stockdale wasn’t a very adept political candidate, but his record of courage and resilience nonetheless set him far apart from the politicians he was running against.

Greitens’ book stands as undated wisdom on one of humankind’s greatest challenges: how to react positively, with the force of life, when much of everything seems to be going the other way.