evidence: Mark Twain wrote the above in The Innocents Abroad, a travel book published in 1869 detailing his excursion by boat to Europe and the Holy Land. [...] Another quote attributed to Mark Twain is: [...] I concur. I’ve had some opportunities I’ve passed up, including watching the annual 4th of July fireworks from the World Trade Center towers many years ago; that opportunity is gone forever. I’ve visited the Leaning Tower of Pisa, and felt too rushed to wait in line to climb the tower itself; chances are I’ll never be back. I regret not doing those things. But I can’t recall too many things I did that I regret. They didn’t always work out well, but the experience is a memory for life.