Only Atlético de Madrid (Santiago Bernabéu, Liga BBVA game), Olímpic Xàtiva (first leg of the Copa del Rey) and Borussia Dortmund (second leg of the Champions League quarterfinals) have managed to keep a clean sheet against Ancelotti's Real Madrid this season. Real Madrid have played 55 matches and to score in 52 of them is simply a brilliant statistic. That's 94,5% of the matches ending with a Real Madrid-goal.
Furthermore, in those three games the BBC was not together. Benzema, Bale and Cristiano only played for 30 minutes during the 0-1 defeat against Atlético. Against Xàtiva, all three missed the game, while Cristiano Ronaldo could not play in Dortmund.
If Real Madrid score today, Bayern Munich will have to get three goals in order to advance to the Champions League Final. Ancelotti is no fool and knows that Real Madrid will probably need to score in order to play in Lisbon.