"From the first test you could see the boy had something about him, because he was simply very good at speed," Ricky Flynn told AAP.
"He was able to take on a huge learning curve, because it's not very similar to Australia. The karts, the engines and the tyres (are different).
"And nothing really fazed him, he just got on with it and didn't moan, and that was that."
Piastri will need those traits and more to become Australia's first world champion in 46 years this season, beginning with the Melburnian's home grand prix at Albert Park on Sunday.
The first of those factors is obvious. Drivers don't win world titles without being fast.
But the other two will be equally crucial as Piastri attempts to avenge last year's late-season fade out that saw his McLaren teammate Lando Norris take the title.
This year will be a learning curve for all drivers, following F1's wide-sweeping regulation changes.
Cars will be 30kg lighter through changes to power units, tyres, aerodynamics and fuel, with Lewis Hamilton labelling the alterations "ridiculously complex".
Change, traditionally, has been good for Piastri.
He won the 2020 Formula 3 Championship in his first year in the cars and backed it up by being Formula 2 champion the following year.
Even when he arrived at Ricky Flynn Motorsport in 2016 with limited karting experience in Europe, a young Piastri adapted fast enough to take podiums and finish sixth overall.
"That was unheard of," Flynn, who has now had five Formula 1 drivers pass through his stable, said.
"It was a whole new ball game for him. And the competition is obviously the best in the world.
"Not only did he have to learn the cars, he had to learn all the circuits and everything else.
"He had a huge, huge learning curve to go through from everything, because obviously he was not at home, not with his parents.
"And he did it."
Flynn spent a lot of time with Piastri that season.
The teenager moved in 10 minutes away in Hertford, just north of London and often drove with him to races.
"Nothing particularly fazed him or was a problem," Flynn said.
"He settled in pretty quick in both England and then obviously the team.
"He picked up sticks to come over to the world's highest category. It was a big ask, but he just got on with it."
Piastri's unflappable approach has been his trademark since his entry to Formula 1 in 2023.
The only time it has shown signs of cracking was late last year, when a horror weekend in Azerbaijan started a run of eight races where he surrendered a sizeable championship lead and ultimately lost out to Norris.
Flynn watched the end of last year as nervously as anyone.
Beyond Piastri, Norris spent three years at Flynn's team and took the karting junior world title in 2014.
But the veteran karting mentor has no doubt over Piastri's ability to rebound in 2026.
"He's got to be stronger after that, because obviously every experience you learn from and get better and stronger," Flynn said.
"I'm sure he's gutted he didn't win it, after leading the points. But I don't think it'll faze him in that he'll crumble in any way.
"He'll take all the positives from it and come back even stronger than he was, because that's the character he is."
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