Ever have a write-off day?
Where stuff happens that leads you to feel like the day's a write-off and there's no point in even trying?
There's no need for that if your best is your goal.
What do I mean?
Although we'll all have days when our great intentions go awry, that should never preclude the fact that you can still do your best.
Your best when things have gone awry may well not be the same as your best when all systems are go, but it'll still be your best.
If your goal is to do your best, and you remember that your best changes by the hour let alone by the day, it'll take the pressure of perfection off your shoulders.
And really, other than weight is there any other area of your life where you wouldn't accept your personal best as great?
The best you can do if you're hungry or have cravings will be different than the best you can do when you don't. The best you can do on your birthday will be different than a plain old Thursday. The best you can do after a really crappy or stressful day will be different than a boring one. And so on, and so forth.
Perfection's an awful goal.
Do your best.