You're never going to agree with anyone in tiresome debates over whether a particular player is "world-class" or not.
Why? Well, it seems as if we all interpret the status differently. While some are more lenient and willing to add anybody in the middle of the purple patch into the illustrious realm, others are far more strict. "They've got to be one of the five best in their position," some will assert.
No matter what you're interpretation of world-class is, there are a few things we can agree upon. Most importantly, these are players who step up in the biggest moments when their teams need them most.
That's what renders the Champions League so significant in regards to player legacy. The brightest of continental lights pits the very best up against the very best, and only those worthy of lofty classifications will swim. Others will filt.
On Wednesday night at the Santiago Bernabeu, the grandest and most daunting of European amphitheatres, four Arsenal players cemented their world-class status.
1. Jurrien Timber

The Dutchman perhaps had the toughest task of the Arsenal defenders on Wednesday night, as he saw plenty of the explosive and unpredictable Vinicius Junior.
The Brazilian found himself on the scoresheet, but there's no denying who won the one-on-one duel. There's not a winger I'd back to reliably beat Jurrien Timber. He's an absolute master when facing up against an attacker.
Timber was aided by a several Arsenal bodies when Vini cut inside, but the Dutchman matched the winger stride-for-stride when he burst towards the byline. Corners were the most he could get out of the Arsenal full-back, who's been consistently brilliant off the back of an ACL tear.
We didn't see much of Timber in possession, not in advanced positions anyway, but that was never going to be his task. He tamed Vinicius over the two legs, and there's not a right-back in world football I'd rather have marshalling one of the Gunners' flanks.
If you're going by the top-five in his position metric, Timber is undoubtedly world-class.
2. William Saliba

The mistake for Madrid's goal was a complete lapse from Saliba, who was caught on the blindside by Vini Jr. The error could've been costly, but it shouldn't cloud what was another supreme performance from Arsenal's centre-back hero.
Life's easier when you've got William Saliba in your team. How many defenders combine his freakish athleticism with outstanding fundamentals? Saliba has long been regarded as perhaps a level above world-class - elite, maybe? - and his showing in Madrid proved why Los Blancos are supposedly determined to sign the Frenchman this summer. Good luck with that, Florentino!
The sequence in the first-half which saw Kylian Mbappe receive possession in behind Jakub Kiwior only to be expertly shunned by Saliba in the box proved to be a tone-setter. His box and recovery defending were exemplary in the absence of trusted centre-back partner Gabriel.
3. Declan Rice

Aurelien Tchouameni, Federico Valverde, Luka Modric, Jude Bellingham, and Thomas Partey were among the midfielders who took to the field on Wednesday night, yet it was Declan Rice who stood out in the middle of the park.
Perhaps we should expect such displays from a £105m midfielder, but how many players have produced performances like that against Real Madrid away from home in the knockout stages of the Champions League? N'Golo Kante was similarly majestic at the Bernabeu three years ago, but only a few have been capable of producing such mastery.
Last week was all about Rice's ball-striking, but the second-leg manifested the very best of the Englishman as a dominant ball-winner and carrier. He manned his zone in front of Arsenal's defence expertly, refusing Madrid to penetrate centrally, and offered his team respite by breaking upfield.
If you're not yet convinced by Declan Rice, I'd suggest taking up golf-watching off the back of the Masters buzz.
4. Bukayo Saka

I didn't include Bukayo Saka in my three standouts on Wednesday night, but the inevitable winger came ever so close. I may have had that missed penalty lingering in the back of my mind.
His woes from 12 yards could've inhibited the winger, but Saka seemingly only grew stronger as the contest wore on. It shouldn't be forgotten that the winger is doing this off the back of hamstring surgery. He hasn't missed a beat since returning to the fold.
He shrugged off David Alaba relentlessly, proving to be far too strong for the veteran defender. The Austrian couldn't get near him, and Saka wasn't deterred by Alaba's early attempt at a 'leveller'.
Arsenal's 'starboy' paraded around the Bernabeu like it was his second home, with his finish in the second-half depicting a superstar at the top of his game.
World-class and more. The best is yet to come.