City host Bundesliga strugglers Schalke on Tuesday with a 3-2 first leg lead in their last 16 tie hoping to avoid the pitfalls that did for Paris Saint-Germain and Real Madrid in Champions League shocks last week.
Guardiola admitted even he was taken aback by Manchester United's stunning 3-1 win in Paris and holders Madrid's capitulation to a talented young Ajax team, but refuted suggestions their elimination had cleared the way for City to finally conquer Europe.
"We are teenagers in this competition that's my feeling. It's not excuses, of course we want to win it," said the Catalan coach on Monday.
"You have to dream and point as high as possible but in the same time you have to accept there are other teams thinking the same with a lot of quality and lot of talent."
Guardiola was annoyed by City's mistakes in conceding two penalties and having Nicolas Otamendi sent off 22 minutes from time in Gelsenkirchen three weeks ago despite turning around a 2-1 deficit with 10 men through late goals from Leroy Sane and Raheem Sterling.
And he used that experience to warn his players against any complacency.
"In domestic competition there is another game, in this competition there is not another game. It is something unique, the focus is incredible and when you make something wrong they (the opponent) punish it," he added.
"Schalke had two shots on target and scored two goals. We played 23 minutes 10 v 11 when we could avoid that second yellow card from Nico.
"We are lucky today we are here 3-2 up when we could be 3-1 or 4-1 down. That's the reality in this competition. (There is) work to do, be calm and focused."
- Gundogan future unclear -
Along with the suspended Otamendi, Fernandinho will again miss out through injury, but the Brazilian's absence has not been felt as badly as first feared due to Ilkay Gundogan's form.
The German has deputised ably in the holding midfield role, but has so far refused to commit his future to City beyond his current contract, which expires in 2020.
"There is no decision yet otherwise I would have signed or rejected a contract. I would say we are still in talks," said Gundogan.
"I'm 28 years old now so obviously my next contract will decide where I am for maybe the end of my career.
"Everyone feels different, (whether) to go for a new challenge or change something. I am always open-minded for challenges, it is not (an) obvious (decision).
"Everyone has to make their own decision and at the moment I try to play as good as possible."
Guardiola, though, urged Gundogan to make his intentions clear.
"I would prefer him to stay but at the same time I want to feel he wants to stay too," said Guardiola.
"If he doesn't want to stay, he has to leave."
Schalke sit 14th in the Bundesliga after a dismal domestic season, but their under-fire manager Domenico Tedesco insists a shock win over City isn't out of the question.
"The situation in the league is precarious but nevertheless we are going to try with all our effort tomorrow," he said.
"We showed in the first leg we are capable of competing with City. We need to play better than we did in the first leg but we want to take that chance."
Schalke finished second in the Bundesliga last season but their form this term has put Tedesco's future in doubt.
Rather than focus on his battle to avoid the sack, Tedesco urged his players to cause a memorable upset against City.
"We have to use the small chance we've got as clear outsiders. We need a special day and hopefully we will have that," he added.