I used to tell my clients to follow the 80/20 rule: be as near to perfect as you can 80% of the time and let yourself be a cake-eating, gin-drinking, non-exerciser the other 20% of the time. Then I did the math.
If we go off the rails 20% of the time, that is 73 days a year or about 6 days a month. That is not cool. If we have a goal, this is not the path to that goal. So, I’ve changed my ratio and now I recommend the 93/7 rule which works out to about 2 days a month of not doing our best and I think that's plenty.
I believe we need to find a balance between being too forgiving of ourselves and too hard on ourselves. There is a sweet spot right between these two approaches. You are not a terrible person if you flub but being tired is not a good reason to not take care of yourself.
Go, Do, Be and do your best 93% of the time.