I too, have days when I am not shooting as well as I would like too. I can with honesty say that those days of inconsistent shooting have, for the most part become fewer and farther apart.
I think one of the things overlooked, or misunderstood is the importance of "calling your shots". In other words, when I miss now, I know what I did wrong by the analysis of where the arrow went.
I am not a bow "Guru", I am someone who spent a lot of time understanding spines, tuning, and other factors that affect where my arrow hits. So when I consistently hit right of the target, I am left handed, I can with honesty say that I have been looking for my arrow in flight/dropping my arm.
While it is our duty to become the best marksmen(and women)that we can, due to factors beyond our control few of us will become "Howard Hill, Ben Pearson, Terry, or you name your favorite". Take your accuracy to it's limit, using all the tools. Tools such as proper arrow selection, maximum tune, because if you are not tuned no matter how great your potential may be you will never reach it.
Some of you are saying what the heck has this got to do with the question on confidence, I say everything. You must have a level playing field to develop confidence, and confidence will come with success. Incorporate the total package of tuning, and good practice. Pour in a little time, and the consistency from day to day will level off to the point where there will be fewer days with inconsistent results.
Again, I am no "Guru", just a few things I have learned that have made a big difference for me.