If you don't succeed at first (they say) try, try again. We're told that persistence always pays off, and that we can do anything once we set our minds to it.
Now while there's nothing wrong with determination, there are times (and days) when you're not going to achieve your objectives no matter how hard you try, no matter how much you grit your teeth.
It would, for example, be plain daft to struggle on with a tree-felling task if the only tool you had was a steak-knife. Better to put the whole thing off until tomorrow then come back equipped with a chainsaw.
The same principle can apply to days when you just can't get things together. Whatever you do, you seem to be taking two steps back for every one you make forwards.
When this happens (and it will) there's nothing wrong at all in postponing the task until you're on better form again.
No sense in flogging a dead horse. Every sense in realising that we all have limits.
Please remember this next time you have one of those days.