If you have attended any event that celebrates an important milestone, like a graduation or retirement, you have heard someone say: “And like Dr. Seuss said, ‘Don’t cry because it’s over; smile because it happened.'” And like many memorable quotations, this is found on all kinds of merchandise: posters, coffee mugs, t-shirts, and so forth. But like many quotes found on the internet, there is absolutely no evidence that Dr. Seuss (the pen name of Theodor Seuss Geisel) wrote it…