In 1968 Jerry Butler sang that only the strong survive. But what did he know? While I'm sure it's true that you, me, we all, often possess more strength than we acknowledge, it's equally the case that now and again there are times when it really is okay to say 'enough's enough'. Times when struggling on with blind and grim determination really makes no sense at all.
Now I'm not suggesting that we all just give up and go home. Far from it. Not for one second. Life is for living, and to live it to its full extent generally takes persistence and tenacity. It's just that it's equally sensible at times to recognise that we've more on our plate than we can deal with. When that happens, to extend the metaphor, for goodness' sake don't pile more on - and preferably offload some of what's already there.
If the next day or two are looming over you with impossible demands, recognise that impossible means just that. Impossible. And actually, you know, saying No to things, and re-scheduling where you can, does take strength. So perhaps old Jerry had it right all along.