Well of course the goal is to win the treble every season at the moment. I'm not denying that. However saying a domestic double (won while playing on a ridiculously high level and setting several records in the CL and the league) and a CL semifinal is a failure and if Guardiola only repeats that, there'll be issues is nonsense. Some people make it sound like the treble is the norm and not an incredible success and failing to reach that norm means letting go of the manager. It's not like I lack confidence or trust in the players, remember me saying that we'll win the World Cup all throughout the tournament, even after the Algeria game? I expect something similar from the players at the club. But if you have countless injuries and see that your players are burned out and the mentality just isn't at 100%, then you simply have to accept that and challenge again next year. Demanding to write history seems a bit stupid, demanding success and hoping to write history is fair enough.
Also I don't think that Ancelotti winning a 3rd CL is comparable to defending the CL, let alone the treble. It was inevitable that Ancelotti, Mourinho or Guardiola achieve that with the way club football has changed. As long as those three keep working at one of the top clubs in Europe, we'll see it again and I wouldn't be surprised if one of them ends his career with 5 CL wins. Doubt we'll see more than 1 CL title defense in the next 10 years though, if we see one at all.