There is a poster I've seen somewhere that says, "When you come to the end of your rope, tie a knot and hang on."
I think when you've come to the end of your rope you should acknowledge it. Say, "I'm done." Then you should let go and hope to fall into a vat of chocolate. Indulge and wallow a bit. Then climb out. Grab your fuzzy pajamas and a wine (alternatively you could fall into a vat of wine and then grab chocolate). Then I think you should be able to say "I had a crappy day. I'm not doing anymore today. I'm not hanging on to be brave or to save face. I am just done. Tomorrow I will attempt to climb the rope again. But I'm not just hangin' in there anymore."
And I think you should not feel guilty about that attitude or the indulgences.
That's what I think.