In the context of Europe, we're not going to win it, so have we to be depressed any time we don't win it? What point do we have to progress to in the tournament before we can be disappointed at going out, but happy with how far we got?
As a supporter, there are two ways to look at where we are; with perspective and without. Either outlook makes fück all difference to how to team performs on the pitch, so the 'undermining our traditions and attitude of success' line in the OP is pîsh.
Nobody is celebrating that we're out or that we got beat, but while being disappointed people are at least satisfied that we're making progress and en route to being back at the point of only being happy when we win. You're torturing yourself by pretending we should be winning everything when clearly we're not yet at that point in our recovery, the only thing you're undermining is yourself.
It's the same as the 'we must win the next 5 games' line that get's thrown out constantly. It's fine to say that and it meets the 'attitude of success' requirement, but it's unrealistic in our current situation. Why convince yourself that it's a guarantee only to be pissed off when it doesn't happen?