It's not though is it? The system works otherwise we wouldn't have won numerous trophies and broken countless records using it. Like all systems though it's not infallibile, none is. If one was then a team would win every game and all the trophies they competed for.
Players have off days, make mistakes, your opponent just plays a fantastic game and you lose. It happens. Yesterday in spite of having some key players missing and struggling with a lack of a proper pre season we still should have been at least ,3-0 up in the first 20 minutes. Pep can't put those chances away, nor can he defend better as Ake should have for their goal. Sure it was a counter attack that undid us, but we could play a more defensive system and still lose. I'll agree against certain teams he should be a little more pragmatic at times but he seems to be doing that now.