Suffocating pressure and Garbine Muguruza once again stand between Serena Williams and a record-equalling 22nd career major when Wimbledon gets underway on Monday.
Williams is a hot favourite to secure a seventh title at the All England Club and draw level with Steffi Graf on the open-era major leaderboard.
But the American was also a hot favourite to match Graf at last year's US Open, only to falter in the semi-finals against unfancied Italian Roberta Vinci when a rare calendar-year slam beckoned.
Williams also stumbled trying to equal Graf's benchmark tally in the Australian Open final against first-time grand slam finalist Angelique Kerber.
Then she blew her big chance in this month's French Open title match against Muguruza, the newly-installed world No.2 who lost to Williams in last year's Wimbledon final.
Chinks are starting to appear in Williams' armour and so too are doubts creeping into her mind, tennis greats suspect.
"Something is holding her back - and it could be nerves," said 18-times grand slam champion Chris Evert.
"Especially against Kerber and against Muguruza, she wasn't able to dig herself out of the hole like she has in past years.
"She's been famous for finding that next gear, that next level, when she's down."
Three-times Wimbledon champion John McEnroe expects Williams to finally catch Graf this coming fortnight, but says the pressure must be mounting.
"It's not easy to try to do what she's doing, to make history at this stage," McEnroe said.
Williams is making no secret of her disgust at flopping in the French Open final and the fiercely-competitive veteran remains bent on rewriting tennis history three months shy of her 35th birthday.
"I'm going to take a moment to be super honest ... I was really pissed," the world No.1 said in a video posted online three days after succumbing to Muguruza at Roland Garros.
"I was pissed, I have to admit.
"I thought I could've played better. I thought I could've competed better. I thought I could've really done everything five times better - and I didn't and I was so pissed that I actually abandoned my racquets in France after maybe a few smashes of the racquet bag."
Muguruza, for her fearless shot-making, athleticism and power, and Kerber, for her dangerous left-handed grasscourt game and confidence that comes with grand slam success, shape as Williams' biggest dangers.
Muguruza is seeded second for a final rematch with Williams, but history is against the 22-year-old Spaniard.
All-time greats Graf, Evert, Navratilova, Evonne Goolagong Cawley, Margaret Smith Court, Billie Jean King and Williams are the only women in the 48-year open era to have won the French Open and Wimbledon back to back.
Two-time champion Petra Kvitova also can't be dismissed, while Madison Keys is the undoubted dark horse after winning Eastbourne and cracking the top 10 for the first time.