It is amazing. A man could walk into your office and tell you a tale of how his morning has been. A true horror story, three simultaneous flat tires in the rain on a highway with a closed shoulder, spilt coffee in his lap, difficulty sitting down after his alien abduction, you name it. All you have to say is "At least it's Friday," and he will instantly perk up. How has medical science not spent millions of dollars researching this phenomenon?
Where does the therapeutic nature of this phrase gather such strength? I bet even if the stock market crashed on a Friday, they wouldn't even call it a "Depression" until Tuesday (What? Too soon?).
Try it. Today being Friday, you could probably walk up to a stranger you pass on the street and punch him in the stomach. "Sorry, pal. Hey, at least it's Friday." And boom, no repercussions. I am unable to figure it out. Maybe the harmonic nature of the syllables as they are strung together creates some euphoric state in the brain of anyone within earshot.
I will warn you, though, "At least it's Friday" does NOT carry the same weight unless it really is Friday. I tried it on a Tuesday not too long ago and rather than cheering up said coworker, I received puzzled looks. "It's not Friday," was all I got from her as she walked away.
Lesson learned.