The man in the baseball cap and hoodie may be Australia's 17th richest individual but is scared of being found out as an impostor.
As a keynote speaker at TEDxSydney, Mike Cannon-Brookes  confessed he suffered from impostor syndrome and most days felt like he did not know what he was doing.
"Have you ever felt out of your depth, like a fraud, and just kind of guessed-slash-bullshitted your way through the situation, petrified that at any time someone was going to call you on it?" he said on Friday.
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"It's not a fear of failure. It's not a fear of being unable to do it. It's more a sensation of  getting away with something, a fear of being discovered, that at any time someone is going to figure it out.
"And if they did figure it out, you'd say to yourself, 'well, that's fair enough actually'."
Mr Cannon-Brookes said when he and his partner, Scott Farquhar started their IT company their main aim was not to wear a suit to work but success brought complications.
Hiring their first HR manager, he did not know what questions to ask and later, attending board meetings in a T-shirt, he found himself  "surrounded by suits, acronyms flying around and feeling like a five-year-old as I write them down secretly in my notebook so that I can look them up on Wikipedia when I get home later".
"For me impostor syndrome is a feeling of being well out of your depth. Internally you know you're not experienced enough or qualified enough to justify being there. Yet you are there. And you have to figure a way out because you can't just get out."
The Australian Financial Review's 2017 Rich List named Mr Cannon-Brookes, 37 and a Sydneysider, as the nation's 17th most wealthy individual with a personal fortune of $2.51 billion. He co-founded Atlassianâ, a collaboration software company that helps teams organise, discuss and complete shared work. More than 68,000 organisations â including eBay, Twitter, Coca-Cola, Visa, BMW and NASA â use Atlassian's products.
Mr Cannon-Brookes joked he had met his wife posing as an impostor.
A weekly commuter to San Francisco some years back, he was in the Qantas lounge when she approached mistaking him for somebody else. He did not disabuse her of her initial impression.
"Classic Aussie bullshit became some sort of forward movement and a phone number ... a decade later she is my wife and we have four children," he said.
Mr Cannon-Brookes thought most successful people "felt like frauds" but the key was to realise they were out of their depth and harness self-doubt as a force for good.
Recently, when South Australia had a power crisis he saw something on Twitter that Tesla thought it could solve the situation so he fired off some tweets only to see the media descend on him as "some sort of expert in energy".
At the time, he said, he did not know the difference between a AA battery and 100 megawatt battery.
"A chronic case of  impostor syndrome ... I remember thinking, 'I've kind of started something here I can't really get out. If I abandon the situation, I could set back renewables in Australia and maybe look like a complete idiot on Twitter'. All I could do was to not freeze and try to learn," he said.
He ended up brokering talks between Tesla boss Elon Musk, South Australian Premier Jay Weatherill and PM Malcolm Turnbull on the nation's energy shortages.