What is it about this year's season that has seen two contestants quit I'm A Celebrity?

For the first time in the show’s history, stars on Australia’s I’m A Celebrity… Get Me Out Of Here! are calling it quits.

It was big news last week when tennis player Bernard Tomic uttered the eight magic words – “I’m a celebrity, get me out of here” – barely three episodes in.

It was, after all, a first for Australian TV, and one that involved tennis’ most notorious “bad boy”.

Then, on Thursday night, we watched boxing champion Anthony “The Man” Mundine do the very same thing.

That’s not one, but two contestants, pulling the plug less than a fortnight since the premiere aired on January 28.

Just like that, Channel Ten – who no doubt paid big bucks to lure the pair to the show – lost their two biggest drawcards.

Considering in all four seasons this has never happened before, it’s only natural that Australian viewers are reacting angrily. This wasn’t what the fans signed up for. And how could Mundine and Tomic have given up on the $100,000 they were supposed to be competing to win for charity?

But speaking to Mamamia, Australian sports psychologist Jeffrey Bond warned against calling them “quitters”.

“It is all too easy for the ‘armchair experts’ and the television watchers to believe they know the answers when they really have no idea what is going on in the mind and lives of the person they are unfairly labelling,” Bond said.

LISTEN: We take a look at the biggest problems with this season of I’m A Celeb, on our pop culture podcast. Post continues after audio.

Still, the situation begs the question: What’s so different about this year that’s resulting in celebrities dropping out?

It comes back to the decision to cast two of the biggest egos in Australian sport. It was always a risk. Previous seasons have seen AFL players and swimmers including Brendan Fevola, Dane Swan and Lisa Curry on the show, all of whom played by the rules. But Mundine and Tomic are men who have always thumbed their noses at the status quo.

On the one side, we have 25-year-old Tomic, who after a troubled year not qualifying for the Australian Open, announced, “I just count money, that’s all I do. I count my millions.” More recently he has been labelling Tennis Australia “corrupt” and lashing out at Lleyton Hewitt for snubbing him from the Davis Cup team.

On the other, there is 42-year-old Mundine. A man who declared himself the “the uncrowned best athlete of all time” in 2015, and who is renowned for spouting homophobic and sexist tripe. He’s been open about his support for capital punishment for LGBTQI people, and has said that women shouldn’t wear skirts above the knee.

Certainly, Mundine and Tomic have different personalities, different motivations. But they do have two important things in common. Firstly, the unmistakable egos. Secondly, they both come from very solo sports.

The effects of competing alone should not be underestimated. In 2016, a study of 361 athletes by Germany’s Technical University of Munich found that individual athletes were more likely to develop depression – with symptoms including guilt, sadness and suicidal feelings – than team players.

The same study found solo athletes were also more likely to feel ashamed by failure and harshly blame themselves, The Guardian reports.

Tomic himself recently touched on the toll that the solitude of tennis had taken on him.

“I didn’t have a childhood, I didn’t have a life since I was eight, nine-years-old,” Tomic said on I’m A Celebrity.

“I think people just don’t realise that tennis is a very isolated sport, it’s an individual sport — it’s not soccer or basketball where you can rely on your teammates.”

Australian sports psychologist Jeff Bond told Mamamia that tennis was an "an extremely individual sport... And there aren't too many other sports where your ego is on display and under scrutiny all of the time when you're out there."

Boxing is in many ways very similar. A high-pressure sport, with a passionate fan base, in which all responsibility lands squarely on one person's shoulders.

To succeed in these sports, athletes often need a fervent belief in oneself. They need an ego.

Which brings us to the egos of Mundine and Tomic.

"Both of these athletes - like many other elite performers around the world - have very strong egos," he said.

"So one suspects that if they found themselves in a situation where they do not have control and their egos are there for many others to see, they will bail out if it looks like they might not be successful. Tomic has a history of ‘tanking’, so this could simply be another example."

Bond said that elite sportspeople with big egos tend to immerse their core self-worth into their career. And when the going gets tough, they become fragile.

Before joining I'm A Celebrity, Tomic's tennis career was already struggling. Then, reality TV viewers watched him become rattled by a challenge that saw him suspended over a cliff. He stumbled away, saying he felt like vomiting and that joining the show was a bad idea.

“I just wasn’t expecting all of this, you know. I am just not coping well,” Tomic said.

The very next day, he was gone.

In Mundine's case, he threw in the towel just days after his boxing rival Green was introduced to the camp, and one episode before audience-voted eliminations would begin.

Sports psychologist Patsy Tremayne, an Associate Professor at Western Sydney University, told Mamamia she wouldn't be surprised if putting Mundine together with his long-term opponent had a negative impact. Two rivals do not want to show weakness to each other.

"Two rivals do not want to show weakness to each other," she said.

On Thursday, Mundine appeared unnerved when fellow campmate Jackie Gillies suggested he "might be voted out" in favour of Green.

“Listen, if you’re voted out before Danny Green, then we know who’s liked,” Gillies said.

He eventually left after being forced to spend 15 minutes in a room full of snakes with Green.

"I just don’t want to be here anymore," he said. “I know I’m going to get a lot of votes. I don’t want to take people’s spot.”

Of course, like anyone, these men are complex characters and we can't be so simplistic as to blame just ego and their individual sports for their short-lived I'm A Celebrity appearances.

Tomic has spoken honestly about how much he was battling feelings of depression.

Meanwhile Mundine spoke of missing his family, fighting back tears as he spoke of his children.

But by casting Mundine and Tomic, Ten took a gamble. These two are the "rebels" of Australian sport.

"These are individuals who are used to going against the grain. Other contestants might have wanted to go out, but they wouldn't actually go ahead and do it," Tremayne said.

When you have the ego to convince yourself your decision is right, it's far easier to remove yourself from a situation than to face failure.

For years, they have faced criticism for their actions and their views. Why would they stop now?

Mamamia reached out to Channel Ten for comment, but they declined to respond.

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