Patrice Evra knows at first hand the damage complacency could do to Manchester United's bid to reach the Champions League final.
Only a heavy defeat to Schalke at Old Trafford next week can end their hopes of playing in a third final in four years after their 2-0 win over the German side in Gelsenkirchen on Tuesday night.
It seems highly unlikely yet Evra knows the improbable can sometimes turn out to be possible, as his own career shows.
"In football you never know," said the France defender. "I remember playing for Monaco in the 2004 quarter-final and we played in the Bernabeu against Real Madrid and lost 4-2.
"Real thought they were going into the semi-final. They thought they were there already. But in the second leg we won 3-1 and went through."