Without bragging I am pretty good at what I do for a living. So when I struggle as everyone does its frustrating. Lots of people feel this. You know what you are capable of and the level of your production is well above goal on a very consistent basis then it puzzles you.
Of course there are forces outside your control that can and will impact how you do so as the old saying goes you have to roll with the punches. Everyone has a bucket of some sort to fill in their line of work and its great when its filled daily. The goal is to do your best as to fulfill your expectations but never to put your coworkers down in the process.
Keep reminding yourself that tomorrow is another day to get it right and to consistently produce.