What Cristiano Ronaldo has achieved in football goes beyond comprehension.
Having scored over 600 career goals, won over 20 career honours and bagged the Ballon d'Or title on five occasions, he will rightfully go down as one of the greatest players in history.
His achievements at Manchester United, Real Madrid and now Juventus will be remembered for years to come and he will endure alongside legends like Diego Maradona, Lionel Messi and Pele.
However, it's easy to forget that everything started for Ronaldo at Sporting Lisbon, his boyhood club for whom he made 31 appearances before moving to Old Trafford.
Although football fans are more than familiar with that pre-season performance that stunned Sir Alex Ferguson, his displays across the 2002-03 campaign aren't often documented.
Ronaldo at Sporting Lisbon
It was the big opportunity for the legendary Portuguese to experience first-team football, featuring in the Primeira Liga as Sporting battled their way to a third-placed finish.
Part of that very squad was Spanish forward Tonito, who never really hit the same heights he did with Sporting but still remembers playing alongside Ronaldo before his career stagnated.
And as part of an interview with Gazette dello Sport, he has recounted training with Ronaldo and has described his notorious work ethic, even back in his teenage years.
Tonito on Ronaldo's dedication
Tonito explained: "Cristiano was a kid, but he was just like the man he became: humble, ambitious, determined and professional beyond belief.
"During training, he'd turn heads among the veterans, and I'd say to him: 'Steady, don't overdo it...'
"I would also give him lifts [to and from training].
"But I'd have to wait an hour at the training ground, because he never wanted to leave.
"I'd bang on the window of the gym and say: 'Come on, Cris, it's time to stop - it's getting late!"
Even at the age of 18, Ronaldo was displaying the kind of determination we've become used to and the list of former teammates singing his praise is getting longer and longer.
Although stories of Ronaldo's dedication to training have been abundant at United, Real and Juventus, this serves as one of the biggest indications that the forward was commitment from the start.
And no matter where you sit on the Ronaldo vs Messi debate, you can't help but point towards the former as the ideal example for training determination.
From his early days at Sporting and his new challenge in Italy, it seems Ronaldo is always giving 100% to get to the top and stay there. Brilliant stuff.
Do you think Ronaldo is the greatest player in history? Have your say in the comments section below.