Right now, there's a gap between what the band can do and what the band actually does. The reason that the band failed to qualify for the final on Saturday, put simply, is that when we went onto the competition field some bottles crashed, and the play just didn't live up to the preparation.
And it's a fairly consistent thing: everything sounds fine in practice, but when we go out for performance it's noticably worse, when we go out to compete it's worse again, and when we go out to a Championship it's worse still.
The downside to that is that there's not a huge amount you can do about it in practice. As noted, when we're practicing things sound fine, because everyone's in their comfort zone and the confidence is high. It's when the pressure is on that the confidence goes... and you can't practice for that pressure situation without the pressure, for obvious reasons.
Simply put, confidence is gained by doing difficult things well. So you do the practice and the preparation, because that gives you the very best chance, but then you have to go out and perform. And then you have to do it again, and again, and again. And, likewise, you go out and compete, and hopefully each time you compete you get better, and you gain confidence, and so you get better, and so it goes. (And that applies in pretty much every field. To gain confidence, do difficult things well.)
There's a flip side to this, of course, and it's a killer: confidence is much easier to lose than it is to gain. Because if you go out to do the difficult thing and it doesn't go well, that's going to hurt. And it's going to hurt more if someone proceeds to gleefully point out all the ways it didn't go well. And it's going to hurt even more if that "someone" is the person who should be building up the confidence instead of knocking it down.
It's fair to say I get quite frustrated when I push a learner forward to play with the band so they can gain experience and confidence, only to have the powers-that-be in the band proceed to tear into them for every single little thing. If they weren't making mistakes, they wouldn't be "learners". Grr.
And since I'm on a nearby topic, here's how to give criticism. Firstly, you want to 'sandwich' your criticism: you want two positive comments and one constructively-negative one. Start with a positive, then the constructively-negative, then finish with the positive. The positives can be nice and general - "yeah, that was pretty good". The constructively-negative needs to do three things: (1) it needs to be specific, (2) it needs to highlight not just what's wrong but also how to fix it, and (3) it needs to hit the highest priority. If there's a whole mess of stuff needing addressed, tackle the most important once first, then tackle the next one. (And don't do the "round robin" of picking one the first time, then something else the second, something else the third, and then back to the first. That has the double-whammy of both confusing people and giving the impression that they just can't get anything right.)