“Nobody reads a mystery to get to the middle. They read it to get to the end. If it's a letdown, they won't buy anymore. The first page sells that book. The last page sells your next book.”

Variant: I always read the last page of a book first so that if I die before I finish I'll know how it turned out.
Source: When Harry Met Sally

Source: Clockwork Princess

Friend of My Youth (2017)

Shut Up, You Fucking Baby

Source: Inkspell

As quoted in "Literary Censorship in England" in Current Opinion, Vol. 55, No. 5 (November 1913), p. 378; this has sometimes appeared on the internet in paraphrased form as "Censorship ends in logical completeness when nobody is allowed to read any books except the books that nobody reads"
1910s
Context: Any public committee man who tries to pack the moral cards in the interest of his own notions is guilty of corruption and impertinence. The business of a public library is not to supply the public with the books the committee thinks good for the public, but to supply the public with the books the public wants. … Censorship ends in logical completeness when nobody is allowed to read any books except the books that nobody can read. But as the ratepayer is mostly a coward and a fool in these difficult matters, and the committee is quite sure that it can succeed where the Roman Catholic Church has made its index expurgatorius the laughing-stock of the world, censorship will rage until it reduces itself to absurdity; and even then the best books will be in danger still.

Source: The Deeper Meaning of Liff