It ain’t what you don’t know that gets you into trouble.

Daniel McCoy
5 min readJul 17, 2020


Samuel Clemens, aka Mark Twain

I do love a good Mark Twain quote.

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.”

One thing I really love about that quote is how it kind of spirals in on itself if you try to track down where Mark Twain said it, because it just ain’t so, he never said that.

But it’s still a great saying because we all believe things that just ain’t so. It’s impossible for a human to fact-check absolutely everything that they think they know. The real trouble is in that know for sure part.

Photo by Mikael Kristenson on Unsplash

We all need to find a way to cultivate some humility about what we think we know so we are open to new information. I used to know that Mark Twain said that saying above. But I’m something of a nerd for quotes on the internet and when I read the well-researched page about that quote on the Quote Investigator website, I didn’t dig in my heels and resist it. I acknowledged that the source of the saying is tangled and muddy. What I thought I knew turned out not to be so.

I was thinking about this subject because I came across an article where scientists were investigating the cognitive mechanism behind the truth of that folksy saying. The ability to think about one’s own thinking processes is important. We can know things, but we have to leave the door ajar for more and better information to allow our minds to be changed. Self-reflection and self-doubt are important things to be cultivated.

Certainty is a feeling we can all have, but it is just that, a feeling. The fact that you’re certain is not information about your correctness. It takes a lot of work to actually know anything and a lot of work to even know where to look to know anything. Good scientists who have deeply studied a field for decades are still prone to using qualifiers like to the best of our knowledge because they know how easy it is to be wrong about something and how hard it is to be justifiably certain about anything.

One thing I’ve noticed is that just about any subject you drill into properly usually leads to a realization that it’s more complicated than that. Water boils at 100 degrees C or 212 degrees F. That’s a fact. But in reality, the exact temperature depends on the atmospheric pressure and what impurities are in the water. That’s one reason why a Cajun cookbook might need a little adjustment for Denver. It’s always more complicated, even in simple recipe physics.

Some of the people I have the most respect for are people who have managed to change their minds about important things that they thought they were sure about. The people at Life After Hate are a great example, people who have managed to escape from the certainty of racism. Politics is strange in that a politician who changes his mind is often labeled a flip-flopper. While actual flip-flopping, changing your mind back and forth all of the time, might be a bad thing, taking in new information and new ideas, and updating your beliefs is a good thing. The idea of a politician who has never changed his mind scares me. None of us have all of the information at any time, so we always need to be open to information that is new to us and ready to adjust our thinking accordingly. Even a seasoned expert can sometimes learn from the fresh eyes of a newcomer.

Much more dangerous than changing one’s mind is certainty, what you know for sure because there’s always a chance that it just ain’t so. Excess or unwarranted certainty is rampant in the world and leads to problems in many areas. Certainty is a strong feeling that the human mind is prone to, but to trust that feeling is a trap that we often fall into in the modern world. Dogmatic belief systems operate on certainty and do not allow for new information to shift those beliefs.

Photo by Andre Mouton on Unsplash

The world is a complex place and our large-scale human society only compounds that complexity. There is far too much information for any one person to know and process. We all believe at least a few things that just ain’t so because it’s impossible for anyone one of us to know enough to really be certain of anything. The only way to cure ourselves of those just ain’t so beliefs is to be open to new facts and ideas and not cling too firmly at what we think we know.

Photo by Sourabh Barua on Unsplash

The great success of the human species is largely due to humans relying on the knowledge of each other. In comparison studies between human children and other primates, the humans excelled at tasks where cooperation, sharing of knowledge, and trusting the knowledge of others added an advantage. The chimps and monkeys had to learn things for themselves which limited them to the amount of information they could handle alone. The human advantage, what makes us human, is each other. Our success as a species is the amount of knowledge we can amass together, not alone. Trusting the feeling of certainty in ourselves is a roadblock to that advantage. Being a fully functioning human means being open to new information and new ideas.



Daniel McCoy

I took a tech job at a place that turned into a movie studio.