I think it's fair to say we've all had shitty days in our lives. Some of us are unfortunate enough to have rendezvoused with a few more then we would care to remember.
When life smacks us in the face with days like this we have two options:
1) Let it take hold of our day/week/month, and allow it to suck the happy moments away
2) Chalk it up to a bad day, slap a smile on our faces, and keep trucking
Neither of these options are easy when you're feeling down in the dumps, but remember; 'it takes 17 muscles to smile, and 42 muscles to frown'. So unless you're looking for a good face work-out I feel it can be easier to opt for smiling :)
In life it is not the cards we are dealt, but how we play them! If it wasn't for these 'shitty' days, our good days wouldn't feel so great. You can't appreciate the calm without a storm every now and again.
It's your approach towards these obstacles that makes the difference. Just remember, as a wise Irish man said:
"We're all in the gutter, but some of us are looking at the stars." - Oscar Wilde