While I love my job and have always felt lucky to be paid for doing what I like best in life, I have come to appreciate the need to have interests outside the workplace. Fridays are the door to weekends where I can explore those interests. On any happy Friday, I feel sorry for those who don't work. It's like asking how anyone could appreciate a sunny day if they've never known a week of rain. My friend Jan laughs when I say that.
Every day is a vacation day.
She's right, of course. But if you want to test the hypothesis behind TGIF, observe the reaction of most workers on Friday afternoon. I've found that many people are more cheerful on Friday. They seem happier and certainly more agreeable. My good mood makes me a bit more generous.