People don’t know what they don’t know, but they do know what they do know. And so when people want to help, train, teach, or educate others they default to the stuff that’s already in their head.
That’s fine as far as helpfulness is concerned, but it means you’re often missing a crucial piece: what the other person actually needs to know.
Humans want to help, and humans usually want to talk. We also leap to information that sounds relevant, even if it isn’t necessarily helpful. If a friend tells you that they’re learning to fly a plane and you happen to be a chemical engineer, you might start telling them what you know about jet fuel. That feels relevant – jet fuel is part of flying a jet, right? – but it has nothing to do with the skills they need to fly a plane.
The very first thing people need to know is “how do I get from point A to point B?” Everything else, even things that are in the same general information sphere, are roadside attractions. When you’re teaching, keep it in mind.
The Opportunity Machine 