It only counts if it can be wrong

There is a principle in science called the Falsifiability Principle. It says a good claim should be testable and capable of being proven wrong. If there is no scenario where your idea could fail, it is just belief.

I lived this during my PhD.

My research focused on imaging the eye. And at one point, I found a way to detect signs of Alzheimer's disease by looking at the retina. That might sound surprising because Alzheimer's is a brain disease. But it turns out the eye can reveal a lot about what is happening in the brain. And the method I was working on had not been explored before.

So we tested it. We took a subject without Alzheimer's, applied the method, and looked at the results. There were no signs of Alzheimer's. The method worked, or at least, it seemed like it worked.

How do we actually know it works? Showing that a healthy person tests negative does not prove much on its own. Maybe the method just shows negative for everyone. Maybe it is not detecting anything at all.

So we had to take someone with Alzheimer's and run the same test. That was the real moment. Because if the method could not detect Alzheimer's in someone who actually had it, then the whole thing falls apart. The method would be wrong. And we had to be willing to find that out.

We ran the test. And it worked. The method picked up what it was supposed to pick up. We put it in a position where it could fail, and it did not.

A claim only means something if it is capable of being wrong. If you never test it against the scenario where it could fail, all you have is a lucky guess.

I think about this outside the lab now too. When someone tells me their business idea is guaranteed to work, I ask, "What would make it fail?" When someone says they are sure about a decision, I ask, "What would change your mind?" If they cannot answer either question, they have not tested their own thinking yet.