At the heart of football's appeal is its simplicity: the team with the most goals wins.
Except that is when it comes to two-legged cup matches, when the away-goals rule kicks in.
Bayern Munich is the latest beneficiary of the rule that makes away goals count double, with Arsenal having nothing to show for ending the German team's 23-game unbeaten run when they met in the Champions League on Wednesday.
A 3-1 deficit from the first leg in London was overturned by Arsenal unexpectedly winning 2-0 in Munich, but the 3-3 aggregate score didn't push the game into extra time as Bayern advanced to the quarterfinals. Had the second leg ended 3-1 the teams would have been forced to play extra time and potentially contest a penalty shootout.
Even Bayern chairman Karl-Heinz Rummenigge acknowledged: ''We were lucky to have scored enough goals in London.''
Two years ago, Bayern fell victim to the away-goals rule at the last-16 stage in the Champions League. Despite winning 1-0 at Inter Milan, the Italian side advanced by winning 3-2 in Munich.
Braga reached its first-ever European final in 2011 by winning 2-1 at Benfica and then clinging on for a 1-0 win at home to advance to the Europa League final with a 2-2 draw.
Tunisia had its place at the African Cup of Nations in January to thank for the away-goals rule. A 2-2 victory at Sierra Leone ensured Tunisia qualified for the finals with a 0-0 draw at home, playing into the hands of those who say the rule encourages ultra-defensive tactics.
Such complaints have been made by Arsenal manager Arsene Wenger - long before his team's title hopes ended for an eighth successive season by exiting the Champions League.
''We proposed to UEFA at some stage that the away goal should only kick in like it does in the (League) Cup - in extra time,'' Wenger said in 2009.
Wenger, though, failed to influence any powerbrokers during his trips to UEFA headquarters in Nyon.
For all the talk of the perceived injustice of penalty shootouts, the away-goals rule now seems to be an established part of the game that is rarely challenged.
But it hasn't always been that way, though.
Before the 1965-66 season, teams deadlocked after the home and away matches either played a third match at a neutral venue, or lots were drawn.
From the 1969-70 season, the away-goals rule was rolled out by European football's governing body for all of its competitions.
And that's how it will remain for Champions League, Europa League and European Championship playoff matches.
''The main reason for introducing the away-goal rule was to encourage teams playing away to try to score and not to defend a 0-0 draw, thus to develop a more attractive football,'' UEFA said Thursday in a statement.
Wenger recalls a time before the away-goal when ''teams went away from home, with no television, played with 10 defenders and kicked every ball into the stand.''
''I believe that the tactical weight of the away goal has become too important,'' Wenger said in 2009. ''Teams get a 0-0 draw at home and they're happy. Instead of having a positive effect it has been pushed too far tactically in the modern game.
''It has the opposite effect than it was supposed to have at the start - it favors defending well when you play at home.''
Yet the rule harks back to the days when securing a victory on the road in hostile environments was an achievement worth rewarding. Now, though, most major teams play slick modern all-seater stadiums, and foreign trips are less uncommon with the growth of the Champions League and Europa League.
Even though the format of the competitions have changed over the years, the away-goals rule appears set to endure.
Rob Harris can be reached at http://twitter.com/RobHarris