Charles Darwin trained himself to write down every fact that disagreed with his own theory, the moment he noticed it, because he knew his own mind would try to make him forget.

He called it a golden rule. Whenever he found an observation that ran against his emerging theory, he forced himself to record it immediately, in writing, before his own conviction could quietly erase it.

He understood something about his own mind that most people never examine: unpleasant facts fade faster than pleasant ones. A finding that confirms what you already believe gets remembered easily. A finding that contradicts it gets explained away, minimized, or simply forgotten — not through dishonesty, but through the ordinary way a mind prefers to be right.

Charlie Munger, one of the most successful investors of the last century, said this exact habit was one of the reasons Darwin succeeded where sharper, faster minds of his time did not. Darwin wasn't the most naturally gifted scientist working on the question. He was simply more honest with himself about the evidence he didn't want to see.

This has a name now: confirmation bias. It shows up the moment a trader takes a position. Before the trade, the evidence gets weighed fairly. The instant the position opens, the mind quietly switches sides. News that supports the trade gets noticed and remembered. News that contradicts it gets skimmed past without really registering at all.

A close cousin rides along with it. A win gets credited to skill. A loss gets blamed on the market, on bad luck, on anything except the decision itself.

Darwin's discipline wasn't natural to him. It had to be built, one written note at a time, against the grain of how his own mind wanted to work.

There's no shortcut past this. You can't simply decide to be more objective and become more objective — any more than Darwin could have just decided to notice what he was inclined to overlook. The only tool that has ever reliably worked is the one Darwin used: write down the case against your own position, before you decide whether to believe it.