Variance is a natural part of life, and it's not a battle that can ever be won. Some days you'll perform amazingly, and others you'll be a lot worse. We'd all like to have as many amazing days as possible, but focusing on those days too much can end up doing more harm than good.
In a sense, though, the good days will take care of themselves. On my worst days it seems like I need everything to be just right, but on good days almost everything can be wrong and I'll still produce good work. Good days are going to be good days, no matter what.
A common pattern you see people in is to have a few good days followed by abysmal days. Tons of work followed by almost nothing for days or weeks. This is particularly frustrating because they know they're capable of good work-- they're just not able to extract it from themselves.
On the other hand, some people are able to set a lower bound on how bad days can get. They have just as many bad days, but those days still move them forward a couple squares. That adds up to a lot over long spans of times.