The 6 inches between the ears. And dwelling on the past. A missed target is in the past, can't do anything about that but if you keep thinking about, it will have company. Maybe instead of looking at an event as 100 targets, try looking at it as 100 one target events.
I find breaking mid 90's in singles pretty achievable. 97's and above depending on club and targets thrown fairly often. Getting over the hump for a 100 takes a good solid effort that will tire me out mentally because of concentration and good shooting habits. The mental drain only lasts a short time and I'm ready for next event no problem. I'm the kind of guy if I'm shooting well I don't change my demeanor. I'm talkative between rounds and continue whether I'm 25 or 75 straight.
Once I get through the first couple of shots without error and missing a target I get in the groove. Sometimes I am going straight and I get this feeling that I'm coming off the rails. I start busting targets in large pieces or splitting them in half, it feels like an impending doom. I may have this feeling for 2 or 3 posts and then I drop one I get real solid and that nervousness/anxiety seems to go away. For me this can happen on the first trap through the 3rd. Once I get through the first 3 traps I'm pretty good shape on the fourth trap.
If you are like a lot of us shooting once every couple weeks makes it really hard to be consistent.
The big dogs and a lot of want to be big dogs shoot every week, thousand targets a week will help a lot.