Sport isn't just a game. It's a very serious business and the performers - the athletes, the players, the swimmers - are under immense psychological pressure.
When they crack, the psychological hurt can be more painful than a physical injury. The injury is severe but invisible.
So it was with Monique Murphy.
She started swimming with the Tuggeranong Vikings at the age of six. The pool became her life. "At 10 and 11, I started winning medals," she said.
She had hopes of representing Australia, perhaps even at the Olympics. She was training more than seven times a week, two hours a session. "Swimming became my identity."
And then she crashed. Her performances in the crucial competitions were below what she felt she could do.
"I had lost a lot of belief in myself. I thought I wasn't going to make it.
"I had all the potential but my mental state came out in a physical state. I left the sport knowing I hadn't reached my full potential."
A year later, she had a terrible accident. She fell five floors from a balcony and was lucky to survive. The injuries meant her right leg had to be amputated.
She doesn't know how it happened. It was, she says, an accident. Nobody else was there. She thinks her drink had been spiked.
But from that low point in her life, she has risen. She won a silver medal for Australia in the Rio Paralympics in 2016.
She swam the nine kilometres of Lake Burley Griffin in Canberra in November in one hour and 56 minutes, with her father alongside in a kayak.
But more than that, she is a "Community Custodian" for the Australian Institute of Sport and Lifeline, the organisation which helps people with deep, potentially suicidal mental issues.
In effect, she's an ambassador, telling the world that mental illness in sport has to be recognised and that it should not have a stigma.
That word, "stigma" keeps recurring. There's a lot pressure on elite athletes of all types and a lot of pressure not to reveal inner turmoil.
Athletes by nature are extreme personalities, a lot of them, and there is not a culture of talking about things in the athletic world.Gearoid Towey
Ambitious players want to be selected and worry that any admission of weakness will tip them off the team sheet.
Some sports have a very macho image - football and rugby in their different codes - and mental illness might be seen as male weakness.
But even the most rugged of sports are now showing signs of recognising that mental illness isn't a weakness. Some stars have revealed their inner turmoil.
Tragically, sometimes it emerges too late.
The wife of former AFL star Danny Frawley talked about her husband's depression after he had died in a single car crash. Nobody thought any worse of him and she said he would have wanted her to be open with the public about his state of mind before his death.
But the culture of silent anguish diminishes but doesn't vanish.
"Athletes by nature are extreme personalities, a lot of them, and there is not a culture of talking about things in the athletic world," according to Gearoid Towey, a former world rowing champion with Ireland who is now based in Sydney.
He recognised another problem for sports performers: their careers are often behind them in their thirties. They have to transition into ordinary, unglamorous life.
He set up "Crossing the Line" to help others negotiate that rocky route. He's worked with the Western Sydney Wanderers Football Club and the New South Wales Institute of Sport.
"You go from the huge highs of taking part in sport to the big lows that follow when you cannot compete any more," he said.
"Even if you tell them it is going to be alright, tell them what depression feels like and not to feel bad about, it is a common thing, it is something that happens."
The consensus among researchers is that there's as much mental illness in sport as outside it.
But Dr Richard Keegan, a sports psychologist at the University of Canberra and the author of Being a Sport Psychologist, said that the types of illness in sport tend to be different because the pressures are different.
In cricket, a single mistake can cost the team the game. "As a batsman or a bowler, you're on your own," he says. Players in many sports are on tough contracts - "If they are not playing, they don't get paid."
But Dr Keegan thinks attitudes towards mental health are changing for the better. "It's being repeated more often now that we are allowed to talk about it."
The more we talk about it, the more we can break down stigma.Monique Murphy, swimmer
The Australian Institute of Sport says it's addressing the problem. It's appointed clinical psychologist Mary Spillane to advise it on mental health.
She said that a survey of 750 sportsmen and women revealed that one in three "were experiencing a level of stress that would require professional intervention.
"That is consistent with the general population. Just because they are very good at playing sport doesn't mean they are immune,' she said.
But problems are often different. Social media abuse intensifies pressure on very public people. Fans feel they know the sports personality and that they have a right to an opinion, both for good but also poisonous ill.
The institute has set up a network of experts and advisers.
"They can link with us and we will link them with a psychologist or a psychiatrist," she said.
The swimmer Monique Murphy feels strongly that people have to look after each other. Have a good relationship with a coach, she says, so he or she is "aware of the warning signs".
She remembers her own trauma.
"I was suddenly experiencing all this stigma". A lot of people she thought were close disappeared from her life.
"The more we talk about it, the more we can break down stigma," she said.
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