In the case of Pep Guardiola, everything that isn't winning the Champions League is seen as a failure, yet it's not like that in reality.
It is true, however, that Guardiola has a problem and it's called La Masia and Barcelona. That extraordinary generation of football players raised in the Blaugrana's academy (Lionel Messi, Xavi Hernandez, Andres Iniesta, Sergio Busquets and co) that took him, in addition to how is own coaching talent, football philosophy and leadership skills, to the position of being the 'fu*king master' to use the words he uttered when describing Jose Mourinho.
In his time at the Camp Nou, he managed to win the sextuple. An achievement that had never been seen before, he raised football to the maximum it could be. Season by season, until he left the club full of success. His reputation had been enhanced forever, although improving on what he had achieved at Barcelona was unlikely, perhaps impossible. Since then, the maximum demand for Guardiola has been to win everything, and when he fails it all collapses. His only option is to win; there's no margin for error.
With his words in the pre-match press conference ahead of the Tottenham Hotspur clash, he was wrong. Saying that he wasn't hired to win the Champions League simply isn't true. However, that's one thing and saying Guardiola is a failure is another.
Guardiola's eliminations in the Champions League since leaving Barcelona haven't been at the hands of just anyone. He's made the semi-final three times and lost to Real Madrid, the Blaugrana and Atletico Madrid.
With Manchester City he has fallen at the round of 16 stage to the Monaco side of Kylian Mbappe, Radamel Falcao, Thomas Lemar and Fabinho, before they were eliminated by Liverpool in the quarter-final of the 2017/18 season. Pep, of course, has to bear a large part of the responsibility, but even he couldn't predict that Aymeric Laporte would give away two priceless away goals. It's not all Guardiola's fault.
It's true that Manchester City have spent more than 600 million euros in signings since Guardiola arrived; 608 million euros to be exact. However, he's not the only coach who uses such fortunes and can't win the Champions League. The same figures, and higher, have been invested by other clubs over the same period and none have lifted the famous trophy. Barcelona, Juventus and Paris Saint-Germain have spent 613 million euros, 617 million euros and 634 million euros respectively.
So, it's not just Guardiola, but he does have a problem.