It is a mental thing, especially with the last couple of targets when you are doing well.

I have been on track for a couple of 300-60X NFAA rounds and choked in the last 2 ends, ending up with a 300-57X instead of 60.
Keeping your mind focused for every arrow can be challenging and thinking about your score or how you are stacking up is the beginning of the end.

Been there, done that.........and have the T-shirt to prove it