One day in isolation does not define anything is a common thing said.
So if you have one ‘off’ day, where you are not feeling at your best, then no big deal. Take a break, leave things and go and do something different. We all need a day to switch off at times.
One great day does not define anything either.
So if you have one great day, do not expect everything to be great from there on.
One day followed by another day of the same thing, by another day of the same and so on defines our futures.
It is the repetition of good or bad choices that makes the difference, not one day.
If you want better outcomes and a better future, you do need to keep that momentum going, however, and that is why one day is, in fact important, not for the outcome of that one day, but for whatever you did that day to make a better future. To keep the momentum going, or to make a small adjustment, or to learn a lesson.
It’s a paradox that can only be managed by doing some small thing every single day that is defining your future. Even if it is a bad day, still do one thing, a tiny step towards the future you want.
One day on its own will not build it, a collection of days will. But if you don’t do at least one small thing each day, then the momentum gets broken.
So no matter what sort of ‘one day’ you’re having always do at least one small thing to build your future. The outcome of that ‘one day’ does not matter it is the collection of ‘one days’ that matter.