Source for image, before I added the words: http://saanichfusionfc.ca/wp-content/uploads/2015/06/Lightning_over_city.jpg
Source for the quote, itself: More Maxims of Mark, By Mark Twain, ed. Merle Johnson (New York: Privately printed, November 1927). See, also, this website.
I am grateful to my friend Tom, for helping me correct this Mark Twain quote, an earlier (and apparently incorrect) version of which I posted here.
Regarding the incorrect grammar in the quote: it’s Mark Twain. One does not correct the grammar of a great writer!
RobertLovesPi.net 
I think that “there is too many fools” is Ok, as “too many fools” can be viewed as singular. The more common form being “there’s too many fools”, it is similar to “there’s a lot of fools”.
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My guess is that the (mis)quote I posted earlier was the result of someone being presumptuous enough to try to correct Mark Twain. Had I known this at the time, I would have posted the original version.
A similar thing happens with “TANSTAAFL,” which stands for “There aint no such thing as a free lunch.” This acronym was made famous by Robert A. Heinlein (considered by many to be the greatest science fiction writer of all time), as well as Milton Friedman, who won a Nobel Prize in economics. I once taught economics, and was shocked that the textbook I used (in a different school district than the one I teach in now) dared to correct the grammar of this phrase, and its famous acronym, to “TINSTAAFL,” which that textbook explained stood for “There is no such thing as a free lunch.” My immediate reaction was to have my students change this back to “TANSTAAFL” in all of their textbooks — in ink, no less. Authors of mere textbooks should not be so presumptuous as to correct the grammar of someone who is a great author, or a Nobel laureate, and I wanted my students to know that, and remember it. I stand by this decision, for I believe it was absolutely correct.
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