The only thing to be sure about with the Champions League, is that nothing's for sure.
That is at least what Liverpool fans will be telling themselves as Jurgen Klopp's men prepare to try to overturn a three-goal first-leg deficit against Real Madrid at the Santiago Bernabeu on Wednesday.
Carlo Ancelotti continued his habit of terrorising Liverpool as his team staged a comeback of their own, recovering from 2-0 down at Anfield to run out 5-2 winners.
The LaLiga giants also defeated the Reds in last season's Champions League final, and so the hunger for revenge should be strong, but to come back against a team as strong as Madrid seems fanciful... or so it would seem.
Perhaps the most famous comeback in the competition's history is Liverpool breaking Ancelotti's heart in the final in Istanbul in 2005 as they turned around a three-goal margin in six second-half minutes before beating Milan on penalties, and Stats Perform has taken a look at some of the most notable second-leg Champions League comebacks of all-time to see if there is any cause for optimism for Klopp's team.
Deportivo La Coruna v Milan – Quarter-finals, 2003-04
Speaking of Ancelotti's Milan, they had a strange relationship with the Champions League over a three-year period between the 2002-03 season and that famous night in Istanbul 18 years ago.
The Rossoneri won the 2003 final against Juventus on penalties after an astonishingly dull 120 minutes at Old Trafford, before their agonising defeat to Liverpool at the same stage two years later.
What happened in between might have been the most bizarre of the lot, though.
In the last eight of the 2003-04 season, Milan eased to a 4-1 win against Spanish side Deportivo La Coruna in the first leg at San Siro.
It would turn out to be a strange season for the competition overall, with upsets all over the place, but none as remarkable as Deportivo's turnaround in the second leg at the Riazor Stadium.
Three goals in the first half from Walter Pandiani, Juan Carlos Valeron and Albert Luque put them ahead on away goals, before substitute Gonzalo Fran sealed a sensational 4-0 win in the second half to take the tie 5-4 on aggregate.
Barcelona v Paris Saint-Germain – Last 16, 2016-17
The biggest and arguably most famous comeback in Champions League history, Barcelona looked dead and buried after a 4-0 trouncing at the hands of PSG at the Parc des Princes in the first leg.
Goals from Angel Di Maria (two), Julian Draxler and Edinson Cavani looked to have put the tie to bed before the second leg at Camp Nou had even begun.
Luis Suarez scored just three minutes in to provide hope, while a Layvin Kurzawa own goal just before half-time was followed by a penalty from Lionel Messi just after as the impossible suddenly looked possible.
Cavani scored what seemed to be a crucial away goal for PSG just after the hour though as hopes began to fade for the Catalans.
In the closing stages, head coach Luis Enrique raised eyebrows when he turned to Sergi Roberto from the bench, hardly known for his goalscoring exploits at a time when they needed three in a short period.
Neymar made it 4-1 on the night in the 88th minute with what most assumed was just a consolation, before Barca were given a penalty soon after, which the Brazilian also dispatched.
With seconds remaining deep into stoppage time, Neymar lofted a ball into the box to find Sergi Roberto, who applied the finish and sealed an unbelievable 6-5 aggregate win.
Roma v Barcelona – Quarter-final, 2017-18
Of course, what goes around, comes around and Barca were on the wrong end of a dramatic turnaround just a year later.
Their 4-1 home win in the first leg had them full of confidence heading to the Italian capital for the second.
As with Barca's comeback against PSG, the return encounter started with an early goal, with Edin Dzeko finding the net just six minutes in at the Stadio Olimpico.
The Blaugrana held out until half-time without further damage, but Daniele De Rossi scored a penalty to bring Roma to within one goal of going through on away goals.
With eight minutes remaining, Kostas Manolas headed in a corner at the near post to send the home fans into absolute delirium and improbably take the Serie A side through.
It was a chastening experience for Barca, but surely it was just a one-off...
Liverpool v Barcelona – Semi-final, 2018-19
After a 3-0 win against the Premier League challengers at home, Barca had put themselves in a strong position again, but this time with the caution that was necessary after their humbling by Roma.
Yet again, an early goal gave hope to the optimists as Divock Origi bundled in the opener for Liverpool in the seventh minute, but yet again, Barca held out until the break, knowing Liverpool still needed two just to take it to extra-time.
Those two arrived in very quick succession as half-time substitute Giorginio Wijnaldum made it 2-0 in the 54th minute with a sweeping finish before heading in a third less than two minutes later.
All the momentum was with Liverpool, and with an almost inevitable amount of farce, a quickly-taken corner by Trent Alexander-Arnold caught the visitors napping as Origi slammed in a fourth.
Two seasons in a row, Barca had thrown away three-goal leads from the first leg, amounting for half of the four occasions it has happened in the competition's history.
Manchester United v Paris Saint-Germain – Last 16, 2018-19
While this was not a comeback from a three-goal deficit, it is the only example of a tie in which the team that has played the second leg away from home has won despite losing the first leg by more than one goal.
PSG outclassed United at Old Trafford, winning 2-0 thanks to goals from Presnel Kimpembe and Kylian Mbappe, while Paul Pogba was sent off late on for the hosts.
The dominant nature of the win more than anything else is why few gave United a hope of turning things around in Paris, but once more, an early goal changed the mood as Romelu Lukaku scored in the Parc des Princes with less than two minutes played.
Juan Bernat equalised soon after, but Lukaku restored United's lead on the half-hour mark.
PSG tried to put their English opponents away but in stoppage time, conceded a penalty for handball against Kimpembe, allowing Marcus Rashford to fire home to give the Red Devils a place in the history books.
So where does this leave Liverpool's chances of overcoming a three-goal deficit in Madrid?
Well, Los Blancos have only lost at home by a three-goal margin twice in the Champions League, both in the 2018-19 campaign, going down 3-0 to CSKA Moscow in the group stage and 4-1 against Ajax in the last-16 second leg.
Meanwhile, Liverpool have won an away game in the Champions League by three or more goals on 10 occasions, eight of which have come under Klopp, while they only very recently beat Manchester United 7-0 in the Premier League, albeit that was at Anfield and was swiftly followed by a limp 1-0 defeat at Bournemouth on Saturday.
You could argue that if it were any other team than Madrid, who seem to have a spell over the famous tournament, you would give Liverpool a chance of doing it such is their own record of dramatic appearances in the Champions League.
It seems like an impossible task, but you could also argue that if ever there were an opponent who could do such a thing to Madrid, it may be the Reds, especially given their past with Ancelotti.
It would certainly raise an eyebrow.