Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do.

We searched Twain's books, essays, notebooks, published correspondence, and documented speeches and found no instance of this line; Twain died in 1910, and the saying does not surface in association with him until many decades later, which is a strong signal against his authorship. Our tracing of the fuller passage — "Twenty years from now you will be more disappointed... So throw off the bowlines. Sail away from the safe harbor... Explore. Dream. Discover." — leads not to Twain but to H. Jackson Brown Jr., whose early-1990s inspirational writing collected this material, with Brown crediting the core sentiment to his mother, Sarah Frances Brown. The book database confirms the passage circulating widely only in recent decades (for example, Francis Tapon's *Hike Your Own Hike*, 2006, and Eddy A. Sumar's *The Hidden Dreams*, 2009), always as the same composite motivational unit, never in any Twain-era text. A stray suggestion in our notes tying the line to the Vonnegut family or to Will Rogers and Ambrose Bierce did not hold up — no documented text from any of them contains this wording, so those leads amount to vague sentiment rather than a citable origin. What we do have is a specific, named, documented competing origin in H. Jackson Brown Jr., which is more than mere absence of Twain evidence and clears the bar for a positive alternative source. On that basis, this quote is misattributed.