Working out what makes one person brave enough to risk their lives to save another is quite complex, according to psychologists.
For more than four decades Australia has honoured thousands of home-grown heroes with bravery awards.
Mixed in with the police, emergency workers and soldiers are ordinary Aussies who have selflessly risked their lives saving others from armed gunmen, violent assaults, burning vehicles, floodwaters, and even sharks.
Today, 74 Australians are being honoured, including Tori Johnson and Katrina Dawson, both of whom gave up chances to escape gunman Man Haron Monis during the 2014 Lindt Cafe siege so they could help others trapped inside, but ended up losing their own lives.
But what is it that drives ordinary people to perform acts of bravery?
The answer isn't simple.
Oxford University Press last July published a review of dozens of studies focusing on bravery and concluded that both nature and nurture play a role.
Brave people were more likely to be self-confident, risk-takers, resilient, the oldest sibling in their family, as well a have a good sense of humour and a deep sense of empathy for others, the review said.
Eugene Aidman, Adjunct Associate Professor of Psychology at the University of Sydney and Australian Psychological Society fellow, relates many of those traits back to childhood.
He believes how brave a person is hinges on three elements: a lack of or reduced feeling of fear; their mental attitude toward protecting others; and their "fight or flight" response to stress.
Parents who allow their children to take risks are helping them develop traits that "will ultimately lead to the big bravery acts" later in life.
"Science tells us that fear is learned," he told AAP.
"So you learn from your parents to face the challenges head-on and take them as an opportunity to grow, or be fearful.
"When you are faced with real life-threatening danger you will either flee or fight, and when you fight you might be fighting for yourself or for your mates or someone else other than yourself, and only in the latter case is it a genuine case of bravery."
Hormones may also play a role.
Yale University psychiatrist Deane Aikins found in 2009 that soldiers who stayed calm in challenging situations had lower levels of the stress hormone cortisol, meaning they weren't as scared.
Another study led by Peter Kirsch of the US-based National Institute of Mental Health in 2005 suggested that oxytocin - often dubbed the love hormone - can reduce feelings of fear.
Often after ordinary people have performed a brave act like rescuing someone from a house fire, they talk about how they felt compelled to do it instead of having made a conscious decision to act.
"If you talk to some people who have engaged in these acts of bravery they sometimes say 'I didn't even consider my own safety', or 'I didn't even really think about the fact whether I know CPR or not'," Dr Lisa A Williams, a senior lecturer at UNSW's School of Psychology, said.
"I've yet to see data that suggests that people weigh that up in any conscious way."
For emergency workers and soldiers, deciding to help is automatic thanks largely to their training.
"To them it's not a question of bravery it's them executing the job they are trained to do and of course they value that very highly," Dr Williams said.
However, Dr Williams said sometimes ordinary people do consider the pros and cons before going to someone's aid.
"Among the costs would be the potential personal risk and also, interestingly, the potential embarrassment or guilt of not helping," she said.
"On the benefit side you of course have the benefit of actually potentially saving someone's life or geting them out of a dicey situation, and reputational benefit like a bravery award."
Dr Williams believes Australia's annual Bravery Awards send an important message to the wider community that altruistic acts are valued.
"These types of actions we as a society hold up and admire them often because we think, 'my goodness would I have done that?'"