The Bavarians were completely outgunned as doubles from Sergio Ramos and Cristiano Ronaldo condemned the holders to an ignominious 5-0 aggregate elimination at the semi-final stage on Tuesday.
Guardiola, whose side put up much more of a fight in the 1-0 loss last week at Santiago Bernabeu, sought no excuses for the Allianz Arena humiliation.
"Everything happens in football from playing well," the former Barcelona boss told reporters. "I've have had several hard defeats in my career and this is one of them.
"We conceded goals from set pieces, but we played awful, it's the only reason we lost. There's no other reason, it's just football.
"When you are playing bad, you concede a lot. We came out very energised, it was a back-and-forth game, we could have scored with our chances, but we didn't. Us playing bad is the only one explanation for this defeat."
Bayern, who already have the Club World Cup and the Bundesliga won this season, have one final chance to claim silverware in the DFB-Pokal final on May 17 against Borussia Dortmund, in what will be a repeat of last year's Champions League final.