Knowing What You Don't Know: The Word Howard Marks Removed from His Vocabulary

Thinking· 6 min read

Knowing What You Don't Know: The Word Howard Marks Removed from His Vocabulary

The Magical Word (Or Rather, the Forbidden Word)

Howard Marks isn't the type to speak just to hear himself. In his letters to Oaktree Capital investors, every word counts. And years ago, he made a radical decision: he removed the word "certainty" from his vocabulary.

It's not poetry. It's pragmatism.

Marks realized something most investors (and entrepreneurs) never acknowledge: certainty doesn't exist in the real world. It's an illusion sold by overconfidence.

When you speak of certainty, you're lying. To others, but mainly to yourself.

Why This Matters More Than You Think

Think about the last important decision you made in your business.

How many times did you say "I'm sure that..."?

That phrase is dangerous. Not because confidence is bad, but because it hides reality: you can never be completely sure.

Marks explains it in his writings with brutal clarity:

> "The intelligent investor must recognize that he cannot predict the future with certainty. What he can do is understand probabilities and risks."

When he removed "certainty" from his vocabulary, he replaced it with something more useful: probability, risk, and margin of safety.

This isn't a semantic change. It's a mental shift that affects every decision you make.

How I Applied This Model to My Own Projects

When I launched Find Emergency Plumber, I made the classic mistake: I was "sure" the model would work.

No. I was hopeful. I had researched. But sure? No.

The difference changed everything.

Instead of building as if I knew the final outcome, I started thinking in terms of:

  • **What's the probability this works?** (I estimated 40-60% based on market data)
  • **What's my margin of safety?** (Low costs, rapid iteration, early validation)
  • **What do I need to see to change my mind?** (Clear failure metrics)

This changed how I prioritized. I didn't build the perfect product. I built the fastest MVP possible to validate the hypothesis.

Result: launched in 3 weeks instead of 3 months. And I learned more in the first month than I would have in 6 months of "certain" development.

The Difference Between Confidence and Arrogance

Here's what matters: removing "certainty" doesn't mean losing confidence.

Marks is one of the most successful investors in the world. He has confidence. But it's a calibrated confidence.

The difference:

Arrogance: "I know this will work."

Calibrated confidence: "I have solid reasons to believe this has a good probability of working, but I acknowledge what I don't know."

When you build software, this is critical. Every architectural decision you make has uncertainty:

  • Choose Next.js or Remix? No certainty. Trade-offs and probabilities.
  • Use Supabase or Firebase? Depends on variables you can't fully predict.
  • Scale now or later? You have information, but not certainty.

What smart people do is recognize uncertainty and build systems resilient to it.

Marks' Mental Model: Second-Order Thinking

Marks popularized something called "second-order thinking." It's directly connected to removing the word "certainty."

First order: "If I do X, Y happens."

Second order: "If I do X, Y happens, and then Z, which means Q also changes..."

In other words: recognizing that things are more complicated than they appear.

When I launched my multi-country SEO ranking project (UK and US simultaneously), first-order thinking was simple: "I'll optimize for both markets and rank in both."

But second-order thinking revealed complexities:

  • If I rank well in UK, does it affect my US authority?
  • If I optimize for local UK searches, what happens to my overall organic traffic?
  • If I change my content strategy, how does it affect my existing backlinks?

This "and then what?" mentality is what Marks practices constantly. And it's the opposite of certainty.

How to Implement This Today

You don't need to be a billionaire to use this mental model. Here's the practical implementation:

1. Replace "sure" with "probably"

In your next business meeting, when you're about to say "I'm sure that...", pause. Ask yourself: really? Or do I have evidence suggesting it's probable?

2. Identify your margin of safety

In every important decision, ask: what can go wrong and still result in an acceptable outcome?

For a product: Can I launch with fewer features and still validate the hypothesis?

For a technical change: Can I revert this easily if I'm wrong?

3. Make explicit what you don't know

Marks regularly writes about "what we don't know." He doesn't hide it. He puts it front and center.

In your business decisions, make a list: "These are the 5 critical assumptions. If any of these is false, the plan collapses."

Then design experiments to validate them.

4. Practice second-order thinking

Before making a decision, ask yourself three times: "And then what?"

Am I going to use Claude to automate my workflow? Yes. And then what? My team will be more productive. And then what? I can scale without hiring more people. And then what? My margins improve, but my learning pace might decrease if I don't have friction.

This chain of thinking reveals things that certainty never shows you.

The Price of False Certainty

Marks has watched investors lose fortunes for one simple reason: they were "sure."

Sure the market would go up. Sure the real estate bubble wouldn't burst. Sure Lehman Brothers was safe.

False certainty is expensive.

In software, the cost is different but equally real. Teams that are "sure" their architecture is correct build unmaintainable monoliths. Those "sure" their idea is a winner waste 6 months going the wrong direction.

The Real Superpower

What Marks discovered (and what you can discover now) is that the real superpower isn't certainty.

It's the ability to make good decisions with incomplete information.

That's all we have in reality. Incomplete information. Uncertainty. And yet we still need to act.

Marks does it by recognizing:

1. What he knows (with evidence) 2. What he doesn't know (honestly) 3. What he can control (his decision process) 4. What he can't control (the exact outcome)

This mental clarity is what separates winning investors and entrepreneurs from those who lose.

Takeaway: Remove One Word, Improve Your Decisions

You don't need to be like Marks (though it wouldn't hurt). But you can start today:

Remove "certainty" from your professional vocabulary. Replace it with "probably," "probably with a margin of safety of X," or "I have solid reasons to believe that..."

This simple linguistic change forces you to think more clearly. It makes you more honest with yourself. And it makes you better at making decisions.

Which is, ultimately, all that matters.

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How do you apply this model in your decisions? Where has false certainty cost you? Share in the comments. The best insights come from the real experiences of people who build.