The end of the tennis season perennially produces as many questions as answers.
And one asked repeatedly in recent years, as noted by Roger Federer, is "When will the young guard break through at grand slams?"
Stefanos Tsitsipas has been asked that, too.
The 21-year-old Greek sensation is one of the leading "Next Gen" contenders to end the "Big Three" party at majors next year -- alongside US Open finalist Daniil Medvedev -- especially after capping his stellar 2019 by winning the ATP Finals in London.
But he knows how difficult the task will be.
"It's part of my goals next year, for sure, to win a grand slam title," Tsitsipas told CNN's Alex Thomas after outlasting Dominic Thiem 6-7 (6-8) 6-2 7-6 (7-4) in the season-ending showdown Sunday.
"For it to happen, I will have to go through a lot of pain, a lot of struggle and a lot of hustle.
"I know I'm going to have to figure out things better than them."
Youngest debut winner since McEnroe
While a fatigued Medvedev failed to win a match at the ATP Finals last week, Tsitsipas experienced entirely different fortunes.
He became the youngest champion on his debut at the year-end championships since another player who sported a bandana in his career, John McEnroe, in 1978.
The 6-foot-4-inch Tsitsipas is calmer on court than the temperamental American. But like McEnroe, he is no slouch at the net.
Tsitsipas didn't exceed the fourth round in grand slams in his last three but making the semifinals at January's Australian Open -- coupled with other results -- was enough evidence to suggest bigger things are ahead.
In Melbourne, the former junior No. 1 saved all 12 break points he faced to stun Federer before swatting aside 11 of 12 in downing the Swiss when most of the 18,000 inside the O2 Arena rooted for his opponent in the semifinal Saturday.
Federer gave Tsitsipas a huge compliment afterward, calling him "tough as nails."
If Tsitsipas does make the ultimate breakthrough in 2020, he would become the youngest men's grand slam winner since a 20-year-old Juan Martin del Potro overcame Federer at the US Open 10 years ago.
Federer suspects change might be on the way.
"Does it feel like this year might be the best year yet?" Federer, referring to the "Next Gen," said to reporters. "Possibly.
"But then I look at the list of who finished world No. 1, who has been world No. 1 all these years, and it's just crazy that it's always one of us. But we are not getting any younger.
"So chances increase, not because we are getting worse but because they are getting better, I believe."
Learning from Federer
Tsitsipas grew up idolizing Federer and met him five times this year, if including the Hopman Cup.
"It's still hard to process that sometimes," said Tsitsipas. "I'm in the position where I get to play him so often. And every match I've had against him has been the best lesson I've received playing a match.
"For me, playing my idols, it's insane, because once they used to be my idols and now they are my rivals. It's like a dream come true in a way. It's amazing."
Tsitsipas is surely an idol now himself, especially for those back home in Greece. He is the first and only Greek player to ever feature inside the top 10. The next highest-ranking Greek men's player sits at 446th.
But don't call him "Greek Freak," the nickname given to perhaps the country's biggest superstar, reigning NBA MVP Giannis Antetokounmpo, who congratulated Tsitsipas Sunday.
"Well I don't want to take the title from Mr. Giannis," said Tsitsipas. "He's the first one that got trademark for that.
"But it's great that both of us do such great things in two different sports. We bring Greek people closer, closer to sports, and educate them in a way. It's educational, too, for kids that have dreams, that want to achieve things in life.
"I'm a great ambassador of my sport in my country and really proud that tennis is growing so fast in Greece."