As Mike Tyson memorably pointed out, everyone has a plan until they get punched in the face.
It's a similar story with Kylian Mbappe.
As his opponents have consistently confessed over the past four weeks, nothing prepares you for the pace.
"I had obviously seen him a few times on TV but there is a big difference between watching him and facing him," admitted a visibly shell-shocked Piotr Zielinski.
"On the pitch, he seems even more unstoppable. He is an extra-terrestrial!"
Matty Cash, meanwhile, had done all his homework – and still got schooled.
"I spent the afternoon watching his clips and I knew it was going to be a tough test," he explained.
"But when he gets the ball, stops and moves, he’s the quickest thing I’ve ever seen.
"I’m watching the videos while lying in bed! In real life, he’s burning my legs – that’s the difference."
Hardly surprising, then, that Cash went out of his way to procure Mbappe's jersey after Poland's last-16 defeat to France.
He kept it in the safe in his hotel room, where Lionel Messi's shirt - procured from the group stages - was already taking pride of place.
It's easy to understand why Cash views the jerseys as such prized possessions.
He was lucky enough to secure the most sought-after mementos from facing the two best players in the world at the same tournament.
This chance will never come again. These are two superstars at very different stages of their respective careers.
And yet on Sunday they'll meet in a World Cup final. This kind of thing really doesn't happen very often.
Tyson never got to face Ali for the heavyweight title. LeBron James never took on Michael Jordan in the NBA finals.
And make no mistake about it: Mbappe versus Messi in Qatar is a match-up of such historic sporting proportions.
Messi has already done enough at this tournament to show precisely why he's long been regarded as the greatest to ever play the game.
But Mbappe could not be better placed to usurp the Argentine in years to come.
Two titles by the age of 23 would be sensational. We're talking Pele's level of World Cup legacy here.
At Russia 2018, of course, Mbappe became the only teenager other than the Brazil icon to score in a final.
"Welcome to the club," as Pele wrote on social media after France's 4-2 win over Croatia.
At Qatar 2022, meanwhile, the winger has taken his overall tournament tally to nine. No player has ever racked up as many goals at such a young age.
If he stays fit, then, Mbappe is almost bound to break Miroslav Klose's all-time record, of 16.
He has at least two more tournaments in him, after all. He'll only be 31 in 2030. It's genuinely ludicrous how much he has achieved on this stage at such a young age.
He's already got more World Cup goals than Cristiano Ronaldo (eight) and he's only two off Messi (11).
There are, of course, ongoing concerns over Mbappe's character, fears that he might not realise his full potential because his ego is out of control.
Dani Alves was just to latest high-profile figure to claim that his former Paris Saint-Germain team-mate has yet to learn what it means to be a team player.
"Mbappe is a phenomenon who has not yet understood that those who play with him in attack are a bigger phenomenon than him," the Brazilian told the Gazzetta dello Sport.
"A great player must always know and understand who he plays with, your teammates enrich your qualities."
However, for France, Mbappe is the undoubted star of the team.
Olivier Giroud is the perfect foil for him in attack, making Karim Benzema's injury-enforced withdrawal something of a blessing in disguise, while Antoine Griezmann's incredible industry offers him a free ride from a defensive perspective, allowing him to focus exclusively on what he does best.
It's also worth noting that Didier Deschamps has always bridled at the suggestion that Mbappe is selfish.
Indeed, at this very tournament, the France coach took issue with a question about carefully managing Mbappe which he felt insinuated that he needed to keep the player in check.
"His fitness is fine so we don't need to manage that, so you are saying we have to manage his ego?" a clearly irritated Deschamps asked.
"What do you know about that? I know, but you don't. Kylian doesn't have a big ego, that's not true.
"He's a key player but he's a team player. Of course, he's a star but he's not 18 anymore, he's more experienced."
He's certainly more focused, at least on the World Cup.
Mbappe himself has admitted that the tournament has become an "obsession" for him, that he constructed his whole season, "mentally and physically", around Qatar 2022.
He even refused to speak to the press during the group stage, so determined was he to avoid any possible distractions.
"It was nothing personal against the journalists, nothing against people," he explained.
"It was just that I always have this need to focus on my competition and when I want to focus on something, I need to do it 100 percent and not waste energy on anything else."
Whatever one thinks of that approach, it's certainly paid off for him. And for France.
He has, as Deschamps pointed out, done his talking on the pitch, directly contributing to seven goals on his country's run to the final.
"I knew that he was going to be ready for this World Cup," the French coach enthused. "It is his competition."
It certainly felt that way during the group stage, but one could argue that Messi is threatening to take the tournament away from his club colleague after illuminating the knockout stage.
The stage, then, is perfectly set for a truly titanic encounter between the World Cup's two best players.
Both the Golden Boot and the Golden Ball are on the line in Lusail.
Victory for Argentina would see Messi end the GOAT debate. Victory for France, though, would see Mbappe enter it. At just 23 years of age.