The Need-to-Know principle:
less content, more learning

Most subject matter experts, when you ask them what they want learners to know, will tell you some version of the same thing: everything. They need to understand all of it. And you can see why. When you have spent years building deep knowledge in a field, it feels wrong to leave any of it out. Every piece feels important.

But here is what happens when that instinct drives a learning programme: a 45-minute module that learners cannot get through without losing focus. A course that technically covers everything and practically teaches nothing. A certificate that proves someone clicked to the end, not that they can actually do the job.

Every learner has a limited cognitive budget

There is good research behind this. Working memory — the part of your brain that actively processes new information — is limited. You can hold roughly four things in active processing at once. When a learning experience dumps more than that at you, something has to give. The learner keeps clicking. But they stop actually absorbing anything.

That is not a learner problem. It is a design problem. When you put too much in, you are not giving people more — you are giving them less. You are crowding out the things that matter with things that do not matter quite as much, until none of it gets through properly.

The Need-to-Know principle starts with one question: what is the minimum someone needs to know to do their job competently and safely? Not everything that would be useful. Not everything the expert finds interesting. Just the minimum that makes the real difference between capable and not capable.

A quick test worth running

Here is a test I find useful. Imagine your learner is sitting in an airport, thirty minutes before they board. Something comes up at work and they need to remember what the training covered. What do they actually recall? What can they use?

The answer is almost never the full policy document or the 40-point checklist. It is one or two things that stuck — a decision rule, a scenario that felt familiar, something that gave them enough to act on. The training that lasts is the training designed with that moment in mind, not with a content checklist.

This is why role-specific training almost always beats generic training. A medical device technician does not need everything about regulatory compliance — they need to know what to do when an inspector shows up. A customer service rep does not need the full history of data privacy law — they need to know the three things they must never do with a customer's personal data. Being precise about scope is a form of respect for the learner's time.

How to actually apply it

Start with performance, not content. Before you open a single source document, ask: what does good performance actually look like in this role? What decisions does this person make, and what do they need to make those decisions well? That shifts the question from "what should I cover?" to "what does this person need to be able to do?"

Then audit everything the SME gives you against one question: if the learner does not know this, will their performance actually suffer? If the answer is no — if it is background, context, history, or just interesting — it does not belong in the core module. It might belong in a reference document or a job aid. But it should not be competing for the learner's attention alongside the things that genuinely matter.

And design for retrieval, not coverage. The goal is not to expose people to information — it is to make sure they can actually get to it when they need it. Retrieval practice and application activities do this far better than adding more content. Someone who has practised recalling three things ten times will do better than someone exposed to thirty things once.

The hardest part

None of this is easy, because it means saying no — or at least "not here" — to people who know far more about the subject than you do. That takes some confidence. But your expertise is not the content. Your expertise is how people learn, and what design actually closes the performance gap. Those are different things, and they matter equally.

The best SME conversations I have had start from one shared agreement: the purpose of this programme is not to teach everything we know. It is to close a specific performance gap. Once that is on the table, the conversation about what to include becomes practical rather than defensive.