It happened four years ago, but sometimes, it still feels like it was yesterday. For Paris Saint-Germain, it is an ugly, painful scar that will always be there, regardless of what happens in Wednesday's Champions League round-of-16 second leg against Barcelona. They defeated the Blaugrana 4-1 in the first leg, but the tie won't feel like it's over. On March 8, 2017, the Catalans produced the most memorable comeback in the history of football, beating the Parisians 6-1 at the Camp Nou after losing 4-0 at the Parc des Princes in the first leg.