I think first things first nine times out of ten you need a world class manager or if you are lucky a world class manager in the making i.e. Klopp and Simeone to win the Champions League.
That manager also has to be incredibly tactically flexible because you need to adapt quickly in the Champions League because of the strength of the opposition.
Whilst Pellegrini is a top manager his biggest issue for me is that it's his way or no way, he won't change the way he plays, one of the reasons Wenger has come up short so many times if you ask me.
The personnel needs to be right as well and every team member needs to put the team first and sacrifice himself when needed, you can't have the likes of Yaya Toure, despite his brilliance at times, going around as if the game is a walk in the park, Silva for example needs to learn to track his opposition runs when he has to and Sergio and Edin if played as a two or a one need to be tracking back working hard when not in possession.
To sum it up in regards to us I question whether we have a manger tactically flexible enough and whom possibly overestimates his opposition, I question whether certain players are willing to put the team first and not think individually, and I also question whether we really do have a plan b?
I also don't think we have enough pace in our side when it comes to players and as a team, on the break we look lethargic and show hardly any intent.