This year, the Catalans threw away a 3-0 semi-final first-leg lead against Liverpool as they were thumped 4-0 at Anfield in the return.
Tuesday night's capitulation has, unsurprisingly, caused uproar back in Barcelona as fans and critics try to work out why things went so spectacularly wrong.
Below, we look at the five main reasons for Barca's collapse.
VALVERDE NOT AT HOME AMONG ELITE
Ernesto Valverde presided over what Spanish newspaper Diario Sport described as the “biggest embarrassment in the club’s history”.
If the coach has any supporters left at this point, they will point to the two league titles won during his reign. Impressive achievements, sure, but they must be viewed within the general context of Barca’s eight title triumphs in 11 years.
Barca won the league before Valverde numerous times, and they will continue to win many more when he leaves.
When Valverde’s Barcelona took on a real elite side, as Liverpool are, the former Athletic Bilbao coach’s flaws were exposed.
Why did he pick the same team that started the first leg? Sadio Mane ripped Sergi Roberto to shreds until Nelson Semedo came on at Camp Nou. For some reason Valverde gave the Senegalese the same chance again at Anfield.
Philippe Coutinho, who was abysmal at home, looked even more futile away - but we’ll get to him later.
In last season’s brutal 3-0 defeat by Roma, in which Barcelona threw away a 4-1 first-leg lead, the team’s lack of pace cost them.
This time around Ousmane Dembele was injured, but Valverde would have benched him anyway, and again went for a side bereft of speed. Semedo might have offered it, so might have Malcom. Both started on the bench and came on far too late.
Why didn’t Valverde react quicker? He was impotent as Liverpool smashed Barcelona’s Champions League dream.
“I don't know how this affects my future, we haven't had time to think about those things,” said Valverde. “But here we are and the coach has to take responsibility.”
Meanwhile, president Josep Maria Bartomeu did not want to back Valverde, just saying everything would be looked at when the heat of the moment has subsided.
The coach should not be sacked now - that would be senseless - but despite his recent contract extension, the sensible and most likely solution is that Valverde and Barcelona mutually agree to part ways in the summer, with the Copa del Rey final as his last hurrah.
COUTINHO A WALLFLOWER
Perhaps the worst of Valverde’s selection decisions was to start Coutinho.
The Brazilian wallflower was nowhere to be seen in the first leg but, instead of remembering that and acting on it accordingly, the coach picked Coutinho again.
Predictably he offered nothing at all at his former hunting ground - it was as if Barcelona were playing with 10 men. These days Coutinho can barely cut it against Levante, let alone Liverpool.
Barca's club record signing at €160 million, including add-ons, was withdrawn with the team 3-0 down. It should be one of his final appearances for the club - if Barcelona can find a buyer.
Neither of their two biggest purchases, then, were present at Anfield. Dembele was the other, out injured, again.
Malcom was brought off the bench as an afterthought, while Arthur was also introduced too late.
Frenkie de Jong is on the way from Ajax, which will help the team control the ball better than they did at Anfield, while this defeat may see the Catalans spend big in other positions too.
There will be a shake-up at the club after this epic failure.
MENTALLY WEAK BARCA HAUNTED BY ROME
That the whole of Barcelona’s campaign was based around not repeating the debacle of last season’s 3-0 defeat at Roma, which saw Barcelona throw away a 4-1 first-leg lead, makes this capitulation all the more shocking.
What happened at the Stadio Olimpico in last season’s quarter-final tainted Barcelona’s double win and made the Catalans so determined to triumph in the Champions League that Lionel Messi gave a captain's speech on that very theme at the start of the season.
The 3-0 first-leg lead from an evenly disputed game gave Barcelona a false sense of security, quickly shattered by Divock Origi’s opening goal after seven minutes. That sudden realisation was a hammer blow for Barcelona’s already fragile mentality.
Another salvo after the break saw Georginio Wijnaldum hit two goals in just over two minutes. Even though the score was level 3-3 on aggregate, at that point Barcelona were lying in their grave, waiting for someone to finish them off.
Origi did, putting the finishing touch on Trent Alexander-Arnold’s cunning corner routine.
“For the fourth goal we looked like a schoolboy side,” admitted Luis Suarez. “We have to be conscious that the criticism is going to rain down on us now.”
Barcelona were in a ghost world, haunted by the spectres of Rome, unaware of what was happening around them in the here and now, and Liverpool took advantage.
While clubs like Real Madrid and Liverpool believe they are going to win, against all odds and sometimes against common sense, Barcelona’s ingrained mentality is more fatalistic and afraid. They paid the price.
ALBA & TER STEGEN HORROR-SHOWS
It was cruel and unfortunate for Barcelona that two players who have served them so well this season endured perhaps their lowest moments at the club.
Jordi Alba had a nightmare match, one of his worst in the shirt, giving the ball away in the build-up to Liverpool’s first goal, losing it again for the second.
Marc-Andre ter Stegen was culpable too, with the usually imperious German letting Wijnaldum’s effort squirm under him.
Ivan Rakitic put in one of his most feeble displays of the season, Gerard Pique and Clement Lenglet did not impose themselves in the battle with Origi, and Coutinho, as detailed, was the biggest embarrassment of them all.
Messi could not provide the one killer moment which would have saved Barcelona either.
An away goal was all they needed, one flash of inspiration from the No 10. But he didn’t find the space to do it, shackled masterfully by Liverpool’s dogged defence and midfield. He was offered little help from his ageing strike partner Luis Suarez, either.
Should Messi be castigated? No. He has done so much for Barcelona, been decisive in so many crucial moments, that for once, perhaps it was time for his team-mates to come to the fore.
Instead he was left looking like he only does, historically, with Argentina. Forlorn.
KLOPP'S LIVERPOOL WHIRLWIND
Manchester City coach Pep Guardiola highlighted the quality this Liverpool team have.
“In my career as a manager, I played against incredible sides, there are two that were, ‘Wow’,” explained the former Barca boss.
“One is Barcelona with Luis Enrique, with Neymar, Messi and Suarez up front. The other is this Liverpool. I think they’re the best two sides I’ve faced as a manager.”
Barcelona have not played a team on Liverpool’s level for years.
Real Madrid have been a shadow of their best selves in La Liga and the Copa del Rey, despite their European domination.
Atletico Madrid’s usually rock-solid defence this season has been leaking and, while not easy to face by any means, don’t offer the persistent menace and tireless pressing which Jurgen Klopp’s Liverpool did at Anfield.
Simply put, this Barcelona side were hit by a whirlwind which they haven’t experienced before - even given what Roma did last year.
Manchester United pulled off a similar trick for about nine minutes at Camp Nou in the quarter-finals. Liverpool maintained it for the full 90 here.
And while sometimes overstated, the impressive atmosphere at Anfield was another factor in Barcelona’s nerves.
Luis Suarez’s antics only succeeded in getting Liverpool fans and players more riled up, more noisy, and that didn’t really help Barcelona’s cause.
They needed to calm it down and instead were sucked into the cauldron, where Klopp's witchery had its way.