A BAD DAY IS A GREAT OPPORTUNITY! I love those days when I'm not on, for whatever reason, because it gives me a chance to learn. Remember that every time you shoot you teach your brain something new. When your shots are right on the spot, your brain may only affirm what it is doing. When your shots are off, your brain goes into overdrive to figure out the cause. It might not figure it out during that practice session, however, it will keep working on the problem till you pick up your bow again. Actually, some of the best work your brain does is when you leave it alone to it's business.
Every time you work through a bad day, regardless of how your shooting at the end of the practice session, you minimize the number of bad days in your future. It may actually get worse before it gets better but your brain is solving a problem that probably won't have to be dealt with again. As a number of posters said, "as you go along there are fewer and fewer bad days." So those of us with few bad days should really get excited about one when it occurs. Another chance to learn.
How about a quote that is applicable to many things.
"Consider it pure joy when you face trials of many kinds, for the testing of your "faith" (shooting in this case) must finish it's work to make you mature and complete, lacking in nothing." James 1:2-4