Dover Publications website and possibly apocryphal Mark Twain quote

[Garson O'Toole]

The Dover Books website has advertising material for a reprint of the
volume "Mark Twain at Your Fingertips" compiled by Caroline Thomas
Harnsberger. The first link below leads to what appears to be jacket
copy for the book but might just be an advertisement:

http://www.doverpublications.com/zb/samples/473198/sample62c.htm
http://store.doverpublications.com/0486473198.html

The following quotation is featured at both links:

{Begin excerpt]
Twenty years from now, you will be more disappointed by the things
that you didn't do than by the ones you did do. So throw off the
bowlines. Sail away from the safe harbor. Catch the trade winds in
your sails. Explore. Dream. Discover.
[End excerpt]

This is confusing to me because I explored this saying and concluded
that it was not from Mark Twain. Also, I cannot find this quotation in
the original 1948 edition of "Mark Twain at Your Fingertips". In 1990
the best-selling writer H. Jackson Brown, Jr. published the words
above and credited his mother.

http://quoteinvestigator.com/2011/09/29/you-did/

Has anyone found the above quote in the works of Twain? Has this
quotation been added to the new edition of "Mark Twain at Your
Fingertips" from Dover Publications?
Garson

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