Mark Twain: Trending quotes (page 27)

Part VI: "Two Fragments from a Suppressed Book Called 'Glances at History' or 'Outlines of History' ".
Papers of the Adams Family (1939)
Variant: Loyalty to country ALWAYS. Loyalty to government, when it deserves it.
Context: In a monarchy, the king and his family are the country; in a republic it is the common voice of the people. Each of you, for himself, by himself and on his own responsibility, must speak. And it is a solemn and weighty responsibility, and not lightly to be flung aside at the bullying of pulpit, press, government, or the empty catch-phrases of politicians. Each must for himself alone decide what is right and what is wrong, and which course is patriotic and which isn't. You cannot shirk this and be a man. To decide it against your convictions is to be an unqualified and inexcusable traitor, both to yourself and to your country, let men label you as they may. If you alone of all the nation shall decide one way, and that way be the right way according to your convictions of the right, you have done your duty by yourself and by your country — hold up your head! You have nothing to be ashamed of.
Only when a republic's life is in danger should a man uphold his government when it is in the wrong. There is no other time.
This Republic's life is not in peril. The nation has sold its honor for a phrase. It has swung itself loose from its safe anchorage and is drifting, its helm is in pirate hands.

Not found in Twain's works.
A 1993 newspaper humor column attributes this saying to Reader's Digest: "Picking it up from a Reader's Digest fan, Willie, our ex-shoe shine boy, says some politicians are like diapers. They both need changed often ... and for the same reason."
Also attributed to Reader's Digest in Naomi Judd's 1993 book Love Can Build a Bridge https://books.google.com/books?id=AMmrqZkq3JQC&pg=PA262&dq=%22politicians+are+like+diapers%22&hl=en&sa=X&ved=0ahUKEwiQ2obup6LKAhUBS2MKHfacCmsQ6AEIITAB#v=onepage&q=%22politicians%20are%20like%20diapers%22&f=false: 'A quip I once saw in Reader's Digest said: "Most politicians are like diapers: they should be changed often, and for the same reason!"'.
Not found attributed to Twain until 2010 https://books.google.com/books?id=gNwqfJkXjVsC&pg=PA448&dq=%22politicians+are+like+diapers%22+twain&hl=en&sa=X&ved=0ahUKEwjUq_C6qaLKAhVM7GMKHTuwAfIQ6AEIIzAB#v=onepage&q=%22politicians%20are%20like%20diapers%22%20twain&f=false
Misattributed
Variant: Politicians and diapers must be changed often, and for the same reason
Source: Bill Hastings, "Books, Bricks, Nap's, Tom, , Tres, Tracy ..." https://www.newspapers.com/newspage/14184165/, Indiana Gazette, 1993-09-10, p. 11

Notice
Adventures of Huckleberry Finn (1885)
Source: The Adventures of Huck Finn

Variant: The report of my death was an exaggeration.

In revised edition, Vol. I, "Friday, January 19, 1906, About Dueling.", p. 298, The Autobiography of Mark Twain, 1959, Charles Neider, Harper & Row
Mark Twain's Autobiography (1924)

Source: Life on the Mississippi

Variant: Let us endeavor so to live that when we come to die even the undertaker will be sorry.
Source: Pudd'nhead Wilson

Variant: Be good and you will be lonely.
Source: Following the Equator: A Journey Around the World

Autobiographical Dictation (1906).
Variant: The only reason why God created man is because he was disappointed with the monkey.

Source: Pudd'nhead Wilson

Variant: It's easier to fool people than to convince them that they have been fooled.

Pudd'nhead Wilson's New Calendar, Ch. LXI
Following the Equator (1897)
Source: Following the Equator: A Journey Around the World