However that was the challenge for 1200 students at Queensland's National Young Leaders Day, a leadership day organised by a not-for-profit group called the Halogen Foundation.

Victoria Cross recipient Ben Roberts-Smith, Olympic swimmer Leisel Jones and teen cystic fibrosis survivor Coen Ashton spoke to Brisbane students on Monday about the decisions they made when things got tough.

Corporal Roberts-Smith, originally from West Australia, married a Brisbane woman who went to Ipswich Girls Grammar School, and is now finishing his Masters in Business Administration at the University of Queensland.

However, he is a big, imposing man.

It is easy to imagine him wearing night goggles while silently walking for 10 hours up the 2600-metre mountains ringing Afghanistan's Chura Valley with 80kg of gear - something he did with five five colleagues in 2006 in order to set up a forward observation post.

At that time the Chura Valley was a Taliban stronghold.

Corporal Roberts-Smith received the Medal for Gallantry for his courage as a sniper in Afghanistan in 2006 and the Victoria Cross on his fifth tour of duty in Afghanistan for drawing fire away from his unit while he silenced two enemy machine gun posts.

As he told his stories to the students at the Brisbane Convention and Exhibition Centre you could hear each one of them listening intently.

"What you have to always remember is that no matter what other people say – or no matter what you might feel about a situation – at some point in your life, you will be left with a decision to make about your future," he said.

"And whether you truly believe in yourself or not will be the defining moment."

He said he remembered being told by one of his teacher at school that he would "not make it in the army".

"Now clearly that didn't work out for him," he said to laughs.

"But you know what that did for me? It drove me to want to succeed."

"I did not take that on board as a negative. I said, 'I will not let that come true'."

His height was his next challenge.

"'You can't get into the SAS, you're too tall'," Ben said he was told. "'Big guys don't get into the SAS! It's all little guys.

"Funnily enough, the same thing happened.

"It drove me to work as hard as I could to get into the regiment, to the SAS."

He said there was one important lesson for young people to take from his speech.

"At any one time, any one person can be a leader. And it is up to you to decide your future," he said.

He told of an incident in the Chura Valley in Central Afghanistan in the days after they set up the observation outpost in the mountains when one of his colleagues' actions inspired the rest of his brothers in arms.

Taliban scouts eventually stumbled across the six-man part on the third day of observations.

The men were facing 17 heavily-armed Taliban fighters, with no prospect of aerial back-up.

"We had no choice. We managed to drop the first two, but the third opened fire – he got behind some rocks - and a gunfight broke out," Corporal Roberts-Smith said.

The gunfire drew the attention of the Taliban they were observing. They began to over-run the six-man patrol party.

Two of their six-man patrol team's weapons –including their machine gun - were lost to mechanical failures.

"Eventually the enemy would get to within 30 metres of the observation post on three sides," Corporal Roberts-Smith said.

It was then one of his colleagues – "Matt" – made a decision that turned the tables on the Taliban insurgents surrounding them.

"I realised that at that point we were outnumbered four to one, we were out-positioned, outgunned, about to be over-run, with two broken weapons and we had a man wounded.

"And we had just been told, 'You are on your own'."

Corporal Roberts-Smith said that at that moment he jokingly thought about being an accountant in order to relieve the tension.

"But it was one of those moments when you could feel the fear. And in my opinion, one of the most important traits a leader can possess is the ability to acknowledge their fears," he said.

"The biggest killer of innovation and success is fear. And it shouldn't be."

Ultimately "Matt" scaled a seven-metre cliff on one side of the diggers, drawing enemy fire and allowing the patrol group to hold back the Taliban for two hours until air-support arrived.

It prevented Taliban fighters getting on top of the ridge and being able to fire down on the concealed six-man party.

He said the team ran by their motto "Who Dares Wins".

"Matt believed in our values and on that day Matt was prepared to die for them," Corporal Roberts-Smith said.

"Matt believed that leadership was about making the right decisions because they were right, not because they were easy."

Afterwards students asked Corporal Roberts-Smith a range of questions about his two daughters, his decision to join the army, his workout routines and his future.

St Aidan's student Georgie Hazenbery asked to whom Ben Roberts-Smith would dedicate his Victorian Cross?

"I would dedicate it to the guys I fought with," he answered.

"And the reason why I would do that is because you never fight a battle alone."

Phoenix, a student from Harristown College in Toowoomba, asked what he would say to the teacher who had told him he would never make it in the army.

Corporal Roberts-Smith said he did meet the teacher again when he was invited back to the school to give a valedictorian address.

"Funny enough, I didn't have to say anything," he said.

"He came up to me and said" "You know what I was wrong. And it's fantastic to see that you have achieved."

"And to be honest with you it is much more appropriate and it is harder to be the bigger man and not want to tell people that I was right and you were wrong.

"You let your actions speak for you."

Earlier on Monday 17-year-old Coen Ashton told of battling cystic fibrosis since he was a baby.

He was diagnosed with CF at three weeks of age and has fought seemingly never-ending health problems and been forced to move from Perth to Brisbane to Melbourne for treatment.

"I've spent half my life in hospital," he said.

Mr Ashton's story became a sensation when he decided to jet-ski the 2000 kilometres of the Murray River and sign up 1000 people to Australia's Organ and Tissue Donor Register.

It took him seven weeks.

In November 2012, he had a long-awaited lung transplant operation and has since become an ambassador for Australia's organ donation program.

With his new lungs, he repeated the jet ski trip up the Murray River in 2013.

It took him just seven days.

What message did he have for his young audience?

"It doesn't matter where you come from, it doesn't matter whether you come from a country town, it doesn't matter if you are sick," he said.

"I've got probably the most excuses that anyone could have.

"But it's about taking those excuses and making them your strengths."

National Young Leader's Day was founded by the not-for-profit Halogen Foundation in 1997.

Its guest speakers have featured several Australian prime ministers, sports, business and arts achievers.