The result? A surprisingly high error rate.
A Famous Example (Without Spoilers)
You may already be thinking of a specific problem. One that looks something like this:
A short equation.
A few numbers.
No fractions.
No variables.
No trick symbols.
People answer confidently—and disagree loudly.
What’s fascinating is not which answer is correct, but why so many people answer incorrectly with complete certainty.
That confidence tells us something important about human thinking.
The human brain is not designed to be a calculator. It is designed to be efficient.
Every day, your brain makes thousands of decisions automatically:
Recognizing faces
Estimating distance
Interpreting tone
Predicting outcomes
To do this quickly, it relies on heuristics—mental shortcuts that usually work well enough.
The problem is that math requires precision, not approximation. And when we apply shortcuts to precise problems, errors creep in.
When faced with a “simple” math problem, the brain often:
Skims instead of reads carefully
Assumes familiar patterns
Answers based on intuition rather than logic
That’s how mistakes happen.
The Role of Order of Operations
One of the biggest reasons people get these problems wrong is a misunderstanding—or forgetting—of the order of operations.
Many people remember a version of it from school:
Multiply and divide
Add and subtract
But memory fades, and intuition takes over.
When numbers are presented in a linear format, the brain tends to calculate left to right, even when that’s incorrect. This habit is strong because in everyday life, left-to-right reasoning often works well enough.
Math, however, does not reward “good enough.”
Why Confidence Makes It Worse
One of the most interesting aspects of these problems is how confident people feel about their answers.
