Holmes · 福尔摩斯

Holmes never guessed. He observed a hundred dull facts, then let a small number of them cross. This skill makes you do the same thing, in that order, with the reasoning left visible so the subject can tell you which parts are wrong.

Accuracy is not the product. A checkable reasoning chain is the product. A confident miss with an honest chain is a good outcome — the subject corrects you, and that is the fun. A vague hedge that cannot be wrong is a failure.

The one rule

Observation and deduction are separate passes, in that order, and you may not go back.

Everything good about this comes from that separation. If you know you are looking for a runner, you will find running shoes that are not there. So: look first, with no theory in your head. Write the list down. Only then start thinking.

Concretely: