Talent, athleticism and commitment are not nearly enough to become a Grand Slam singles champion.
Possessing the confidence that you can beat anyone on the biggest stage - where the eyes of the world are fixed on you and there is no place to hide - is arguably the most important characteristic a player can have.
Unwavering belief. Or, as former US Open runner-up Taylor Fritz describes it, delusion.
Fritz is one of the current crop of leading men yet to get his hands on one of the sport's major prizes. The world number 10 is also one of the guys who has blown what looked like a golden opportunity to win this year's US Open.
With Jannik Sinner missing through injury, and Carlos Alcaraz making his comeback from his long lay-off, it felt like a tournament where the leading seeds could capitalise.
Instead, six of the top 10 perished by the fourth round at Flushing Meadows - including Fritz, who squandered a two-set lead against Argentina's Francisco Cerundolo in round three.
"It shows you how even the circuit is, how tight every match is, how difficult it is to win matches," said 24th seed Cerundolo.
"Anything can happen right now."
The dominance of Sinner and Alcaraz - who have won 10 of the past 11 Grand Slam men's singles titles between them - adds to the pressure.
Speaking to the Guardian earlier this year, 28-year-old Fritz said he believes he will feel an "emptiness" at the end of his career if he does not win a Grand Slam title.
World number two Alexander Zverev finally landed his first major at this year's French Open, but revealed afterwards he "could not sleep" and was "not eating" during previous Slam fortnights because of nerves.
Once he released the pressure valve, the 29-year-old German went on to reach the Wimbledon final - where he played freer but still lost to Sinner - and remains in the hunt at the US Open.
Zverev is scrambling through his half of the draw despite being far from his best, but the spectre of Alcaraz - who is getting better with every win - looms large.
"The two-horse race between Sinner and Alcaraz is not healthy for the tour," former Wimbledon champion Pat Cash told BBC Radio 5 Live.
"With every win, Alcaraz is becoming more of a favourite. Four months off, no matches and he could win the US Open."
Pressure is not the sole reason for the leading seeds tumbling in New York.
One argument is that the current top 10 - Sinner and Alcaraz aside - is weaker than it has been for a while.
Illness, injuries and fatigue also contributed at the final major of a demanding season.
Fourth seed Novak Djokovic's ageing body let him down in his shock first-round exit, while third seed Felix Auger-Aliassime put his second-round loss down to suffering dizziness.
Fifth seed Flavio Cobolli said he lacked energy in a third-round defeat, which he attributed to his volume of matches and New York's sapping heat.
Cincinnati champion Arthur Fils lost a tough opener against former world number three Stefanos Tsitsipas, while teenager Rafael Jodar - who has played more than 50 matches in his first full season on tour - looked drained during his first-round exit.
"The season is long. I think all the guys who performed well in the preparation tournaments have it more difficult here," said Belgium’s Alexander Blockx, who knocked out French Open finalist Cobolli.
"We're all human. We're not robots. Every week is difficult. Especially at a Grand Slam where it gets even more physical.
"Mentally you have to really stay in it."
The four leading players locked in a battle at Flushing Meadows for the top ranking adds another element to the dynamic.
Sabalenka has been the world number one for the past two years, but has recently suffered a dip of form which leaves her position under severe threat.
Rybakina is guaranteed to overtake Sabalenka if she reaches the semi-finals, while Pegula and Gauff could pounce if they win the title.
"Looking at the difference between the points in the top 10 compared to the men, you can see how the depth is pretty crazy," said Pegula.
"Everyone has been very consistent and makes it hard to a certain extent [to win a Slam].
"But then you know there's not one or two super dominant players where you feel like they have to lose in order for you to have a chance."
