Tuesdays with Morrie is a shout-out to a little inside joke between Mitch and Morrie. Starting when Mitch was a college student and Morrie was hanging out at the front of the classroom, and continuing through their visits together many years later, they always seem to meet up on Tuesdays. As Morrie says at one point, "We're Tuesday people" (8.33). For whatever reason, this has always been their day, and since the book is a compilation of sorts of their friendship, it's only fitting that it reference Tuesdays as well.