Alex Ferguson once said he considers only four of his former Manchester United players to have been truly "world-class," lauding the talents of Ryan Giggs, Paul Scholes, Cristiano Ronaldo and Eric Cantona.
For Ferguson, who spent more than a quarter of a century at the helm of the English Premier League's most successful side, such players "made the difference" -- transforming a great team into an exceptional one.
His comments were decried by many who said he had even more greatness at his disposal -- such as influential captain Roy Keane -- but there's little doubt the modern game is obsessed with the tag.
Harry Kane is the latest beneficiary, with his Tottenham manager Mauricio Pochettino bracketing the England striker among the "best in the world" after two hat-tricks in a week and three in two months.
"Harry has the profile to be a legend," Pochettino enthused. "Maybe he's starting to be a legend with the goals he's scoring and the way he behaves. He is so professional."
Kane, for his part, was unfazed by the praise. "I feel that if you look at my stats and my goals, then I am up there," he said after last weekend's treble against Stoke took him joint top of the EPL's scoring charts with 17 strikes.
Kane has scored one goal every 106.4 minutes in the Premier League this season. With 0.81 goals per game, the 23-year-old has the best ratio in the division for a player who's played five matches or more.
After missing 10 games with an ankle injury sustained in September, he has scored nine times in eight league matches in 2017 and 12 in all competitions -- a tally only bettered by Barcelona's Lionel Messi.
Yet many neutrals would scoff at the suggestion Kane, who failed to score as England disappointed again at Euro 2016, is among the world's elite.
Some claim a world-class player needs to have also shone at an international tournament, despite the fact Welshman Giggs and Northern Ireland's George Best never played at a World Cup.
Some say a world-class player needs to test himself in more than one league, even though Scholes and Italian defensive great Paolo Maldini never left Manchester United and AC Milan respectively.
Others argue a world-class player needs to win silverware, but even an average player can win trophies in an extraordinary team.
There's always a caveat, anomaly or exception to the rule. For all his 32 major trophies
, Manchester United striker Zlatan Ibrahimovic has never won the European Champions League, despite having played for top clubs such as Juventus, Barcelona, Paris-St. Germain, Inter and AC Milan.
It's a more elusive, indefinable quality, touched upon this week in legendary defensive midfielder Claude Makelele's assessment that Chelsea's N'Golo Kante -- on track to become just the third player to win consecutive EPL titles with different clubs -- won't be deemed "exceptional" until he adds "that aura."
Tottenham's number 10 might not yet have that aura, but Kane is certainly not the "one-season wonder" some suggested.
After scoring just once in his first 13 Tottenham matches last campaign, the academy product quickly went onto silence the critics, finishing the 2015-16 season with the Premier League's Golden Boot. He netted 25 times, four better than in 2014-15 when he was second behind Sergio Aguero.
Fast forward a year and Kane is set to become the first Tottenham player to surpass 20 league goals in three successive seasons since Jimmy Greaves -- the all-time leading scorer in Europe's top five leagues, with 366 before his final top-level game in 1971.
Though not blessed with particular flair or devastating pace, Kane has now hit the back of the net over 100 times in all competitions before his 24th birthday.
So why is a player with more league goals than Karim Benzema, Neymar and Pierre-Emerick Aubameyang since the start of 2014-15 not talked about in the same breath as those stars?
Some contend Kane is a "flat-track bully," only finding the net against inferior opponents, though he's already scored against 23 of the 25 Premier League teams he has faced.
Others say he doesn't do it when it matters, but Kane has 17 goals in his last 17 London derbies, and more against Arsenal -- Tottenham's chief rival -- than any other team.
In fact, the only players to boast a better goal ratio in Premier League history are Arsenal's Thierry Henry (122 minutes) and Manchester City's Aguero (110 minutes).
He may be 194 goals away from all-time record holder Alan Shearer, but the Newcastle great -- now a TV pundit -- is already saying Kane "could break it" if he remains fit and stays at Spurs for the next 10 years.
People keep talking; Kane keeps scoring. And with Spurs sitting second in the table with 12 games remaining -- plus an FA Cup quarterfinal tie against third-tier Millwall -- he has his sights set firmly on ending the season top scorer once again.
"As a striker, you always want to win the Golden Boot," said Kane, who could join Premier League luminaries Shearer, Henry, Michael Owen and Robin van Persie as a winner in consecutive seasons.
"There are a lot of top strikers up there at the minute and there are still a lot of games to play. It would be brilliant to retain it. It is up there in my house and I would like another one."
And that world-class tag?
"If people want to say and write that, I am more than happy."