The Big Short Movie Got the Twain Quote Wrong

Verdict: Misattributed. Mark Twain did not say "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." The Big Short puts his name on it anyway, before the first scene.

Quote in circulation	"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so."
Attributed to	Mark Twain
Seen on screen	Opening title card, The Big Short (2015)
Verified source	None found in Twain's writings
Verification status	❌ Misattributed

Model photo created with AI. The printed line is real.

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The Big Short opens on a black screen. One line of white text appears. "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." Then a name: Mark Twain.

It's a perfect opener for a movie about the 2008 crash. The banks were sure about housing. They were wrong.

Here's the joke. The movie was sure about Twain. It just ain't so.

Where the line really came from

The idea is old. It's older than the movie, and older than most of the names it's been pinned on.

• 1874: Humorist Josh Billings printed a version in his trademark bad spelling. "I honestly beleave it iz better tew know nothing than two know what ain't so."
• 1899: A minister reworded it and credited Twain. It's the first Twain credit in Quote Investigator's timeline. Twain was still alive.
• 1911 to 1977: The line kept moving. It was credited to Artemus Ward, to Billings again, to Twain again, then to Kin Hubbard.
• 1983: Walter Mondale used it in a speech. He credited Will Rogers.
• 2006: An Inconvenient Truth put it on screen with Twain's name.
• 2015: The Big Short did the same.

Quote Investigator traced every version it could find. Its conclusion: there's no solid evidence that any of these famous men coined it. The author is unknown.

The Center for Mark Twain Studies at Elmira College looked too. It found no real evidence Twain said it. One of its scholars called the line "a convenient untruth."

The book got it right

The movie is based on Michael Lewis's book. The book doesn't open with Twain. It opens with a real passage from Leo Tolstoy that makes the same point.

So the movie swapped a real quote for a fake one. In a film about people who skipped the fine print.

What Twain actually wrote

Twain did write about knowing what ain't so. It's a different joke, and it has a page number.

In Following the Equator (1897), Chapter XII opens with this line from Pudd'nhead Wilson's New Calendar:

"There are those who scoff at the schoolboy, calling him frivolous and shallow: Yet it was the schoolboy who said 'Faith is believing what you know ain't so.'"

— Mark Twain, Following the Equator, 1897, Chapter XII

That one is about belief, not certainty. But it's his.

The same book, a better line

Following the Equator has a line we'd rather you live by. It opens Chapter II.

"When in doubt, tell the truth."

— Mark Twain, Following the Equator, 1897, Chapter II

It's the honest answer to the whole Big Short problem. Not sure? Say so.

Years ago, we sold a house with a saltwater pool. The usual advice is to leave during showings. We refused. We're outliers, and we do our own thing.

That's why it sold. The agents hadn't bothered to learn the pool. One couple asked more questions than their agent could answer, so they came to my husband. He knew every detail.

The man who bought the house? A marine biologist. Of course he had questions about salt water.

Knowing beats sounding sure. Shop the sweatshirt → It's also on a mug.

And for the friend who is always sure about everyone else:

"Nothing so needs reforming as other people's habits."

— Mark Twain, The Tragedy of Pudd'nhead Wilson, 1894, Chapter XV

Model photo created with AI. The printed line is real.

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Why it stuck to Twain

Read it out loud. "Ain't." Folksy. A little crooked. It sounds like a riverboat pilot.

That's how quotes drift. A good line with no name picks up a famous one that sounds right. Folksy advice drifts to Twain. Here's how that works.

Before you quote it

You can still use the line. Just don't sign Twain's name to it.

"As the old saying goes" is honest. "Josh Billings had a version in 1874" is honest and more fun.

Want to check the next one yourself? How to Check If a Quote Is Real.

If we can't verify it, we don't print it.

Questions we get

Did Mark Twain say "It ain't what you don't know that gets you into trouble"?
No. Nobody has found it in his books, letters or speeches. The earliest Twain credit is from 1899, from someone else.

Who really said it?
Nobody knows. The oldest close version is Josh Billings, 1874.

What quote opens The Big Short?
This one, credited to Mark Twain. The book it's based on opens with Leo Tolstoy instead.

What did Twain actually say about it?
"Faith is believing what you know ain't so." Following the Equator, 1897, Chapter XII.

More Twain myths: Ted Lasso got one wrong too, and here are three lines he wrote and three he didn't. See everything from Mark Twain.

About the Author

Vickie MacFadden is the founder of Quoteiac. She once sold a house by refusing to leave during the showings. She writes about misattribution because she has to verify every line before it goes to print. That tends to make you notice when other people haven't.

Written by Vickie MacFadden