Indeed, when talking about Champions League matches, the results are always unexpected. Clubs that perform poorly in the Domestic League are actually focused on the opportunity to do better in the Champions League. Therefore, Liverpool should not underestimate Inter who have indeed performed poorly in Serie A. Moreover Arsenal will get a fairly difficult opponent like Atalanta, they were the Europa League champions last season and in terms of Atalanta game is strong enough to make Arteta game plan difficult.
I disagree if you conclude the results of UCL matches "always unexpected". I think it can be true if we say "sometimes unexpected".
IMO, every team should still focus on the domestic leagues until the end of the season. Even if they don't perform well there, it is impossible to put it aside. Each team must try to do their best in their domestic leagues, they have a minimum target to be achieved. For example Liverpool and Atalanta, they must keep their focus on domestic leagues because they will try to finish again in the UCL zone at least.
I agree that Liverpool must be careful with Atalanta. The bad performance in Serie A doesn't reflect the possibility of Atalanta in UCL. They may have bad luck in the early matches in Serie A, but it doesn't mean they will have bad luck in UCL matches as well. Sometimes a certain team has a stronger motivation when they play in UCL or UEL.
. I can say that the result might be unexpected not because of the assumption that club that performed poorly in their domestic league can perform better in UCL( that's totally wrong though) why? Every club that participates in UCL are taken from the selection of top table finishers and I don't expect a team who performed woefully in their domestic league to get selected in the first place. Thus about the result, since the system changed a little them we should also be expecting some new results (so it's still very possible to have an unexpected results this time around) but at the same time I won't be surprised to see the opposite