Norwich manager Paul Lambert admitted his side learned a hard lesson in the 3-2 defeat at home by Watford.
Expectations were high at a full Carrow Road as the Canaries returned to the Championship, but the League One champions were soon two goals behind thanks to strikes from John Eustace and Danny Graham.
Lambert's side improved after the break and pulled a goal back through midfielder Andrew Crofts, but a second from Graham rendered Michael Nelson's stoppage-time strike irrelevant.
Lambert said: "You can't defend the way we did for the first two goals and get away with it. The Championship is new to us and at this level you tend to get punished when you make mistakes, and that's exactly what happened in the first half. But we'll learn from it.
"We have earned the right to be here by winning the league last season, but that's gone now, and we have got to move on at a new level.
"We've just got to put this result behind us, pick ourselves up and start again, starting on Tuesday night when we play Gillingham in the League Cup."
Malky Mackay's Watford side are one of the favourites for relegation this season but excelled on the counter-attack all evening. Lambert said: "You have got to give credit to Watford for beating us; they are an established Championship side.
"But in the second half, I was pleased with the way we regrouped, and we actually played some decent stuff.
"We got our goal back, but then unfortunately the referee failed to spot a push in the lead-up to their third goal, and that killed us. It should have been a free-kick."
Watford manager Mackay said: "The plan was to match Norwich's midfield diamond and to exploit the gaps when we could. More often than not, we took the right option, which you don't always get with young players, and we got our reward."