Amie Du Buisson-Spargo is a drama student set to follow in the footsteps of Grace Kelly and Robert Redford when she starts at the New York acting school they attended. She faced stiff competition – and never let on that she lives with a rare, incurable condition, gastroparesis, that means she can’t eat solid food and must be fed via a tube into her intestine for 10 to 15 hours a day. “I try to do it at night, so that it doesn’t interfere with my day-to-day life,” she says. “It’s difficult, though, since it means I’m connected to a machine on the mains supply and I can’t really move; it’s difficult to get a good night’s sleep. But it’s just one of those things you have to adjust to.”

So, how does a young person such as Du Buisson-Spargo keep going? How does the mum having chemotherapy for a life-threatening cancer get up, make the packed lunches and take the kids to school? How do parents who have lost a child go to work and do the laundry? When others face these daunting challenges, we look on and admire their fortitude. In fact, most of us would do the same if we had to – we are a remarkably resilient species. But the science that underpins resilience is only partly understood.

Resilience is our response to an event that could otherwise impair our normal function. It can be a biological, psychological or social adaptation – or all three. Genetics play a role in how we adapt to a hostile challenge to our health or wellbeing, and early life experiences have an enormous impact: if you wanted to design the ultimate resilient human, you would start with resilient parents, grant the child a secure early life, sprinkle a liberal dusting of money, education and resources and teach them to see adversity as a challenge. You would pay as much attention to their mental wellbeing as their physical health. You would tell them to react to adversity by reaching out. Suffering in silence isn’t resilience – it’s just suffering.

George Bonanno, a professor of clinical psychology at Columbia University, and his team have studied how people cope with adversity. They looked at national data sets and found that, if you measure depression in people before and after major adverse events – such as a cancer diagnosis, a heart attack, chronic pain, trauma or bereavement – about 65-70% of people appear resilient, weathering the painful time without becoming more depressed than they were before. Even people who are paralysed after a spinal-cord injury don’t necessarily become depressed: the same figure, 65-70%, applies.

Of course, that means about one-third of people who experience major illness or difficult life events do develop depression or show signs of not being resilient. “The assumption is that, if you become depressed, you are less likely to take medication or take care of yourself. Depression also fuels inflammatory responses in the body, and vice versa, which increases the damage. If you have a heart attack and become depressed, you are more likely to die than if you have the same type of heart attack but don’t become depressed. If you were already depressed before your heart attack, the death rate is the same as for non-depressed people,” says Bonanno.

Fascinatingly, 10% of people who were depressed before a major adverse event actually stop being depressed when they are diagnosed with cancer or a life-threatening disease. David Westley, an associate professor of psychology at Middlesex University, wonders whether this is because support networks kick in when a person is diagnosed with cancer in a way that may have been lacking before.

Of course, measuring resilience is difficult. There is no single good tool; researchers use a combination of general-health questionnaires, life-satisfaction ratings and scores of subjective wellbeing. Repeated measurements over time are needed, because resilience is the absence of big changes in these scores even when your world seems to be imploding.

A cluster of factors affect resilience, each of which has a fairly small effect. That’s good news, because if you are low in one factor you can compensate with others. According to Westley, social relationships are key. “Resilience isn’t just about the individual; it’s about the family, community or specialist groups that surround them,” he says. “Healthcare professionals should ask: ‘Who would you talk to if you got ill?’ ‘Who would take you to appointments?’ People need to overcome the idea that they must be brave, stay calm or bottle it up. They may equate that with resilience, but it’s not. Bottling up stress prolongs the hormone cortisol, which hammers the immune system and affects memory. Memories become generic and negative, like: ‘Life has always been bad or difficult,’ and it becomes harder to recall times when you’ve coped in the past or things were easier.”

An ability to see stressors such as pain as a challenge, rather than a threat, is also key – and, according to Westley, can actually be taught. He welcomes initiatives in some schools to introduce positive psychology, which teaches the benefits of gratitude, giving and optimistic thinking. He thinks students in particular are under huge pressure, and points to alarmingly high suicide rates among undergraduates. He is piloting a student handbook to encourage small changes that can enhance psychological wellbeing.

Bonanno, though, urges caution. “We need to build healthy habits and behaviours, with techniques such as mindfulness, rather than embarking on a fool’s errand to promote resilience,” he says. Indeed, some interventions have backfired in the past: the Dare (Drug Abuse Resistance Education) initiative in the 80s famously led to an increase in drug use in the US, and the same is true of some educational programmes to cut eating disorders and suicide rates in young people. The US army spent more than $100m (£70m) on a programme to build soldiers’ resilience, but the soldiers hated it, and there is little evidence that it achieved much, according to Bonanno.

Then there is the phenomenon of risk homeostasis, which says that people take more risks when you try to make them act more safely – for instance, the theory that enforcing the wearing of cycle helmets means cyclists take more chances. In a similar way, if you ram resilience down people’s throats, they can become more destabilised, not less. According to Azeem Majeed, professor of primary care and public health at Imperial College London, you can have too much of a good thing: “All doctors need a degree of resilience, but there is a fine line between being too resilient and [being] insensitive.” Even the most robust among us will have moments of fragility and despair. And that’s OK, too.