Liverpool are clear favourites to beat Reading tonight but this is the FA Cup and Benitez knows his team can't afford to be complacent.
"We have to approach the game thinking about winning and not giving them any chances or any confidence that they can do something," said the boss.
"In the Premier League you have to win but if you can't you say 'unlucky'. But in the Cup you have to win.
"The attitude is more important against teams from a lower division. After that you know you have some quality, but attitude is the key.
"This game [Barnsley in 2008] I remember and we were not doing badly. We had some chances and then conceded in the last minute. It was unlucky but it's the same situation now because it's a cup competition - you have to win and can't make any mistakes."