So I was dethatching the front lawn today (don't all of your stories start that way?), when half-way through I realized it was much tougher than I had anticipated.
Me: "This is hard work."
Sam: "Do you need help?"
Me: "Sure! Wanna help?"
Sam: "I'm sorry, I can't."
This conversation totally reminded me of the "Friends" episode when Pheobe gets invited out and says, "I wish I could but I don't want to."