The sleepless nights. Those long walks up to the green. The even longer waits for opponents to putt.
Professional golf has the capacity to bring on nerves like no other sport. And while some of golf's best professionals can attain almost Zen-like levels of concentration, even they occasionally will allow doubts to creep into their thoughts.
Sometimes a distraction turns out to be a blessing.
On Wednesday evening, having attended his daughter Amanda's school graduation ceremony in San Diego, Phil Mickelson boarded a private jet for an overnight flight to Philadelphia just hours before the start of the US Open.
Mickelson landed at around 3.30am on Thursday morning, and managed only three hours' sleep before teeing off just after 7am.
Remarkably, he shot a 67 to lead after the first round. On Friday, having presumably having caught up on a decent night's sleep, he shot a two-over par 72 to still lead the field – along with Billy Horschel – by one shot at the conclusion of the second round.
It is not the first time a family affair has been on Mickelson's mind at the Open.
He carried a beeper with him on the final round of the 1999 Open at Pinehurst in case his pregnant wife went into labour. She delivered Amanda the next day.
Last year, on the final day of the Ryder Cup at Medinah, Rory McIlroy, who had been on Skype to girlfriend Caroline Wozniacki unaware that he had read his tee time wrong, arrived just minutes before his tee-off in the final singles match against Keegan Bradley of the United States.
With little time to prepare, he managed to beat Bradley and play a part in Europe's astonishing comeback win.
Mickelson and McIlroy's cases are examples of how professional sportsmen often have to overcome extenuating circumstances in search of success.
The former Arsenal striker Dennis Bergkamp refused to travel by air after an incident on the way to the 1994 World Cup in the US left him with a fear of flying.
It meant he very often had to travel thousands of miles across Europe from England to play Uefa Champions League games for the Gunners, as well as international matches for Holland.
Bergkamp's brilliance ensured that such inconvenience and disruptions to his routine rarely affected his form. It did, however, mean he occasionally missed matches when the logistics of travel to certain destinations on time became unfeasible.
At least Bergkamp's restrictions were self-imposed. Sometimes even the very best suffer from circumstances beyond their control.
In December 2010, after an air-traffic controllers' strike had forced them into a five-hour coach journey, Barcelona arrived several minutes late for a Primera Liga match at Osasuna. They still won 3-0.
Earlier that year, however, the European champions had to endure a 600-mile coach journey after the eruption of Iceland's Eyjafjallajokull volcano caused major flight cancellations.
Pep Guardiola's team arrived in Milan for a Champions League semi-final with their routine severely disrupted. They performed poorly in a 3-1 loss to Jose Mourinho's Inter, who went on to lift the trophy.
Sometimes the inconveniences are self-inflicted.
The Nigerian squad for the current Confederations Cup will land in Belo Horizonte this morning, just over a day before their match against Tahiti, after refusing to board an earlier flight in a row over bonuses.
It would be wrong, to assume all athletes can easily shrug off personal difficulties. And, in extreme cases, the consequences of forcing sport to be put first can be near-catastrophic.
The truth behind what happened to Ronaldo before football's 1998 World Cup final is shrouded in myth. One thing is obvious; having had a seizure before the match, the Brazilian was in no shape, physically or mentally, to face France, and his performance showed. This was a case of putting a young man's long-term health at risk.
Thankfully, Ronaldo recovered, as many others have in less dramatic circumstances, to put personal woes behind them.
By Sunday evening we will know if Mickelson's sleepless night had inadvertently set him on the road to US Open glory.
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