Monaco qualified for the Champions League quarter-finals for the first time since 2004, going through on away goals after a 3-3 aggregate result against Arsenal in a thriller at the Louis II stadium.
Arsene Wenger, who was returning to the club he coached between 1987 and 2004, was left a frustrated figure after goals from Olivier Giroud and Aaron Ramsey were enough for a 2-0 win on Tuesday night, but not enough to send the North Londoners through.
"We knew it would be very difficult to score that many goals," a philosophic Wenger told BeIN Sports after the tie.
"We weren't realistic enough in our approach and we should have been up by more at half-time.
"At the end of the day, we paid for our performance in the first leg. Monaco were playing at home but didn't have a shot on goal. We were very close, but they surprised us in the first match because subconsciously we were too sure of ourselves," added the Frenchman.
"It's not a question of if we deserved to go through but of being realistic, and we made too many errors in the first leg.
"We have to congratulate Monaco for their place in the last eight as they defended really well. They qualified so 'bravo'! We are on the right track and played the match we had to.
"The last three months we haven't lacked in anything except our performance in the first leg.
"We have a superb spirit and great qualities," added the Frenchman, who helped Monaco win the 1988 French title, the 1991 French Cup and guided the team to the 1992 Cup-Winners' Cup final, where they lost against German side Werder Bremen.
Arsenal were attempting to become the first team in Champions League history to overcome a 3-1 first-leg defeat at home, but came up agonisingly short.
Constant pressure for 90 minutes could have provided more than two goals on another day, but the excellent Danijel Subasic turned in his second straight world-class showing to play a decisive role.
Ramsey, who came on as a substitute and played a key role in putting Arsenal into position to qualify, said there was reason for deep regret after the defeat.
"We've always gone out to Bayern Munich and Barcelona at this stage. But, no disrespect to Monaco, we thought we'd have a good opportunity to qualify, but we gave ourselves a tough test from the first leg.
"It's nearly again, but it's not enough," said the Welshman.
Monaco become the second French team to go into Friday's draw, following Paris Saint-Germain's equally dramatic victory over Chelsea last week, and they will be joined by Real Madrid, Bayern Munich, Porto and Atletico Madrid ahead of yesterday's matches.