Mental and emotional maturity: the 'big three' have it and perhaps the next generation of tennis stars simply don't.
That was, in part, the message from world No.2 Novak Djokovic on Sunday as he attempted to explain why the sport's batch of new stars still hadn't made a grand slam breakthrough.
Seven-time champion Djokovic is a short-priced favourite to win the Open, starting on Monday, with Rafael Nadal and Roger Federer only split by Russian Daniil Medvedev in the betting.
It's a troika which has, in equal parts, enthralled and exasperated tennis pundits who are glad to have three of the all-time greats still around but concerned none of the so-called 'next-gen' has yet to win a major.
Djokovic insisted a number of players possessed the games to do so and weren't far away, but then zeroed in on what he thought were the missing ingredients.
"I think a lot of those next generation players are working very hard, being very professional. That's a good sign because that's one of the precursors, I guess, for the success," he said.
"But, at the same time, to win a slam and also to kind of be consistently on the top level for many years, it takes I think a player to gain that mental and emotional maturity and experience to understand his own strengths, to kind of fight his own fears, to really be able to maintain that level for a long time."
It was something, he said, that he, Nadal and Federer had and which set them apart.
Of the new batch, Medvedev has clearly made great strides, pushing on to world No.4 after registering the most wins (59) on tour in 2019.
Stefanos Tsitsipas has impressed at times but his 2019 semi-final showing at Melbourne Park remains his best performance, while Alexander Zverev has often flattered to deceive and Nick Kyrgios has only performed in bursts.
The fact remains that you have to go back a decade and 41 slams to find a player aged under 25 (Juan Martin del Potro) outside the big three who has won a major.
For Djokovic, who is happy to roll with the cliche of age being just a number in explaining his, Nadal's and Federer's longevity, another figure looms large on Monday.
A victory over German Jan-Lennard Struff in his opening-round match on Rod Laver Arena would make him just the sixth player in the Open era to register 900 wins.
"Milestones are definitely a motivation," he said.
"But at the same time, you know, there's some other higher goals that I have kind of as a driving force, I think, more than any other milestone, I guess."
Djokovic is 2-0 in career meetings with the veteran German, ranked 37 in the world.
Australian Associated Press