I would say the single biggest reason why Barcelona had only 1 European Cup before 2006, is that we have NEVER had a world class goalkeeper. Ever.
Look at yesterday's game. Kobel wonder save at the end to deny Mbappe taking it to extra time and possibly penalties, where it would all be down to the goalkeeper again.
Today, Neuer would have been the difference maker in the tie if they had managed to win. Instead he was the difference maker in the tie with his mistake.
The goalkeeper is by far the most important player in the pitch. We have to be doing better than MATS if you want UCL success. It's that simple.