Why do we hurt, feel self-doubt and constantly struggle throughout life? What does it take to overcome all the obstacles? The bottom line is that hardship is a part of life, but only by facing up to it and learning to tackle all of life’s challenges will we achieve our full potential. So how do you do that? With resilience.

Author Eric Greitens, in his correspondence with fellow Navy SEAL veteran Zach, tries to find the qualities, practices and training needed to become resilient against the harder parts of life. His search took him through history, philosophy and beyond. Ultimately, it seems the ancient struggle we face as humans has a solution that’s equally ancient.

In this summary of Resilience by Eric Greitens, you’ll discover

• how resilience helped create the first modern novel, Don Quixote;
• that people failing to take responsibility for their personal actions helped Nazi Germany; and
• how Ancient Greeks used repetitions to create resilience in both mind and body.

Are you living up to your full potential? The unfortunate truth is, many of us fail to access all our energy, intelligence and compassion because we get bogged down in disappointment and failure.

But we can learn to overcome hardship by harnessing the power of resilience. Because here’s the thing: none of us can escape pain, fear or doubts. But we can refuse to let difficult experiences bring us down! The trick is to see them in the right light. Overcoming obstacles is difficult, but doing so will make you stronger. Simply put, pain builds courage. You just have to be resilient.

That’s what the author learned after spending many years working with veterans. Those brave men and women lost both limbs and friends, not to mention purpose. But by facing the loss and overcoming their pain, they transformed it into something positive.

Consider the story of Redmon Ramos. After losing his leg by stepping on a landmine in Afghanistan, the former marine realized he had two choices: he could either pity himself or confront his pain. He chose the latter option and, as a result, became much stronger. With the help of prosthetics, Ramos eventually entered the US Paralympic Warrior Games and brought home several medals.

There’s a lesson here: the goal isn’t to bounce back from a hardship, but rather to move through it. History is full of similar stories – stories of people faced with seemingly insurmountable challenges and managing to use their misery to their advantage.

Consider Miguel de Cervantes, a Spaniard imprisoned in 1602. To pass time in his cell, he invented a story about an old man who believed he was a knight. Eventually, that tale evolved into the first modern novel, a work of literature beloved to this day – Don Quixote.

We can all follow Cervantes’ lead and meet life’s challenges with courage and resilience.

We all want fulfilling work and happy relationships. But it’s easier to want those things than to get them. And that’s because anything worth having requires lots of hard work and struggle.

But how do you know what’s worth struggling for? Well, it comes down to having a purpose. And that’s not something you can casually find. Rather, you have to forge a purpose by taking action and trying new things.

For instance, take a job in a new town where you don’t know anyone. Or try traveling abroad for the first time. Of course, these kinds of experiences can be painful; leaving your comfort zone is scary.

But remember, challenges won’t hurt you – in fact, we crave them!

Consider the research done by Mihaly Cziksztentmihalyi, professor of management and psychology at Claremont Graduate University. Cziksztentmihalyi showed that the best moments of our lives aren’t passive or relaxing; rather, they’re active – when our body or mind is pushed to its limits. During this joyful state, called flow, we lose ourselves completely in whatever we’re doing.

The crucial point here is that flow arises during moments of difficulty. Meaning, if we’re not being challenged – if everything in our lives is provided for – our minds deteriorate.

Just think of how the body crashes when you don’t meet its basic needs, like sleep, food and water. A similar thing happens when our mind doesn’t get what it needs – a meaningful challenge.

For instance, a 2014 Gallup study showed that after 52 weeks of unemployment, the incidence of depression shot up to 20 percent. Why? The explanation is simple: lack of purpose made people feel unneeded.

In other words, the goal of life isn’t to avoid struggle, but rather to choose meaningful challenges. Because although we can subsist without worthwhile work, we can’t flourish. Not to mention that, in the long run, lack of purpose is as dangerous as deprivation of sleep.

We’ve all been through dark, painful periods characterized by relentless struggle. But how do you summon your resilience and move forward during these moments? Well, start by looking in the mirror.

Because ultimately, resilience is about taking responsibility for your actions. It’s a matter of being able to accept what you cannot change so that you can redirect your focus to things you have control over.

This is an age-old strategy for dealing with life’s challenges. In medieval Spain, for instance, at a time when Jews were severely oppressed, Jewish philosopher Solomon ibn Gabirol wrote that wisdom and peace lie in “being reconciled to the uncontrollable.”

And yet, although you’re not responsible for everything that happens to you, you are responsible for how you deal with it.

That’s what the author realized while visiting a refugee camp, where he saw thousands of men and women struggling to come to grips with a tragic reality. And while some were beaten down by misery, others stood proud; instead of sitting around and mourning, the resilient ones taught children, organized sports games and more. The author saw that even at their most powerless, some people found an inner strength that couldn’t be taken from them.

On the other hand, history shows that there are terrible consequences for refusing to take responsibility for your actions.

Consider the work of philosopher Eric Hoffer, who studies mass movements and fanaticism. When trying to understand why people would voluntarily acquiesce to tyranny, Hoffer encountered a young German who explained that he joined the Nazi party to be “free from freedom.”

For that young man and for others, passing off the heavy burden of responsibility might seem attractive. But that impulse has abetted some of the most notorious acts of tyranny and brutality the world has ever seen.

Imagine a ballet show or a movie: the seeming effortlessness of the final product makes it easy to forget how much work went into it. In the same way, we often don’t realize that good habits and strong character don’t just fall from the sky, but are diligently built through practice and repetition.

Look at it this way: every time we battle our fears, we become more courageous. And repetition ultimately builds resilience, which we can use to overcome hard times.

In fact, the Ancient Greeks were aware that repetition was crucial for forming human behavior. They were also aware that in order to develop a strong character and spirit, you have to train both your mind and your body. Likewise, repetition was a crucial part of physical training in Athens; the exercise regimen was structured around repeatedly lifting stones and running around and around in the sand.

So all in all, if you want to evolve in a different direction, start by changing your habits. Because every time we repeat an action, we’re reinforcing a habit. If you want to become a kind person, get in the habit of being kind daily.

That’s the thing about kindness – it’s a habit anyone can cultivate. It’s a matter of treating your inner kindness as a source of strength, even if you encounter someone who makes you angry or stressed. You’d be surprised to see what effect this can have. Instead of raising your voice and getting upset, just stay calm, kind and compassionate. Chances are, the other person will start acting kindly as well.

Unfortunately, this same principle applies to our negative habits. If we’re mean every day, pretty soon we become mean. And of course, hard times make it easy to fall back into bad habits. Battle this by training even harder to build strong, positive habits.

Sometimes pushing yourself by studying hard or training ferociously is painful. However unpleasant such pain may be, it’s easier to bear, because we’ve sought it out, and, of course, it’s ultimately constructive. But what about those other times – after the death of a loved one, for instance – when the pain finds us. Such tragedies may feel unbearable, but we still have to confront them.

Through his years of work with devastated veterans, the author encountered some former soldiers who tried to numb their pain with alcohol, television or reclusiveness. But the author believes that the best way to ease the pain of veterans is to challenge them. This might involve tutoring a child or training a football team – anything that helps them rebuild a sense of purpose.

Consider the story of Tim, an Iraq War veteran who was struggling to put his life back together after returning home. The author asked Tim one simple, life-changing question: “How are you going to serve again?” Tim said it was the first time since returning home that someone had asked something of him. And so today, Tim owns Patriot Commercial Cleaning, a business that employs other veterans to help them rebuild their lives and re-enter civil society.

Ultimately, you can’t live a full life without purposeful work and strong social bonds. And that’s not only a problem for veterans; living without purpose is painful for everybody. To overcome that pain, you have to find something meaningful.

That’s what the author learned from the years he spent working with veterans and also as a humanitarian aid worker: people need to serve a purpose higher than themselves, especially when things are hard. In other words, outer surface leads to inner growth.

It’s like fighting fire with fire: to help someone overcome their pain and conquer the challenges they’re facing, put a new challenge before them.

Remember when you learned to ride a bike? You probably fell a few times and scraped up your knees before mastering it.

That’s the case for every challenge: at first, you fall. Failure is just the reality and high-achievers have figured out how to live with it.

In fact, those who excel fail more often than those who don’t, because they’ve learned to accept failure as part of the improvement process. Accordingly, they’re willing to try more things and put themselves out there, leading to even more failure. Crucially, these people don’t fail passively, instead finding a way to learn from each mistake.

Many of us fear failure, so accepting it is easier said than done. For instance, many of the author’s former SEAL friends used to be great at boxing, but now they’re unwilling to step inside the ring. Why? Because after tasting success, they couldn’t deal with the prospect of losing.

Nevertheless, it’s possible to overcome the fear of failure at any age. And if you can do that, you’ll be able to try new things, have adventures and grow.

To that end, no matter how old you are, try to see yourself as a beginner. Case in point: after returning home from Iraq, the author – a former boxing champion and Navy SEAL – considered taking up the martial art tae kwon do. But he kept putting it off, wondering whether there was any point to learning a new martial art, since his boxing game was already tops. But when he finally went for it, he got his ass handed to him. Still, he greatly enjoyed learning and realized that defeat is only temporary. And in the meantime, it helps build strength, willpower and motivation.

All in all, failure is a common part of everyday life. And it’s the only way to improve. So, if you’re not failing constantly, you’re probably not trying hard enough.

The key message in this book:

People get better when things get hard. By using our inner strength, we can make the best out of a bad situation. It’s a matter of building up courage, strength and wisdom. In other words, it’s about becoming resilient.

Actionable advice:

Exercise hard.

Find a way to push yourself physically. A truly challenging exercise regimen should push you to the breaking point. Pushing yourself regularly will not only help you feel better in your body, but also awaken your spirit and free your mind.

Suggested further reading: The Road to Character by David Brooks

The Road to Character (2015) explains how society’s focus on fame, wealth and status eclipses moral virtues and internal struggles. This book summary will show you how to reclaim qualities such as kindness, bravery, honesty and commitment.