The Single Affordance Rule
One product, one job. Added functionality can subtract value by destroying clarity of purpose.
- Difficulty
- Moderate
- Time to result
- ~months to results
- Steps
- 5
- Confidence
- 92%
The economically rational view says more functionality means more utility means more value. Sutherland argues the opposite frequently holds: once a product does more than one thing, the buyer no longer knows what it is for, and the purchase decision stops being a simple binary. The design goal is one unambiguous affordance the user can decide about instantly.
Origin
Sutherland credits Akio Morita of Sony, who overruled his own engineers and refused to add recording to the Walkman even though it would have cost about 50 cents a unit. The term 'affordance' is Don Norman's. Sutherland extends the rule to McDonald's menu simplification (versus the customisation-heavy American diner) and Tesla's option list.
Core principles
- 01You want the device to have one function which it performs very well.
- 02Ambiguity of purpose is a conversion killer — the buyer should face a simple binary: do I want that thing or not?
- 03Greater functionality logically implies greater utility and therefore greater value; in practice it often destroys all three.
- 04Choice reduction is a feature, not a cost saving — the McDonald's menu worked partly because it removed choice.
- 05Choice, like novelty, has a right amount: not one colour, but not infinite customisation either.
How to run it
- 1
State the one job in a single sentence
Define the single thing the product is for, in plain language the buyer would use. Sutherland's Walkman version: it is a personal entertainment device for listening to high-quality music on a flight or a train journey, and nothing else.
Pro tip If the sentence needs an 'and', you probably have two products.
- 2
Test every proposed feature against ambiguity, not cost
For each feature request, ask not 'what does it cost to add?' but 'does it make the buyer unsure what this thing is for?' A cheap feature that muddies purpose is expensive.
Pro tip Recording on the Walkman cost 50 cents and doubled functionality — Morita still said no, because it would have made the device ambiguous.
Watch out Engineering teams will argue from marginal cost. That is the wrong axis.
- 3
Make the purchase decision binary
Present the product so the customer can decide in one step: if you want to do that thing, this is the thing for you; if you don't, don't buy it.
- 4
Set choice architecture to the right amount, not the maximum
Where options are unavoidable, offer enough variety to feel personal but not so much that the buyer is paralysed or priced out. Sutherland's benchmark is Tesla: roughly two interiors, two wheel sizes, five basic colours and two premium ones.
Pro tip Configure your own product's options page and notice when you stop enjoying it — that is your ceiling.
Watch out Sutherland's counter-case: configuring an electric Range Rover drives you insane, because by the time you have added everything you actually want you cannot justify the purchase.
- 5
Add functionality only once the concept is culturally familiar
Sony did eventually add recording to the Walkman — much later, when people already understood what a Walkman was. Sequence functionality expansion behind category comprehension.
In the wild
Sony's engineers wanted to add recording to the Walkman. The hardware was already there (it derived from the Sony 'Talkman' dictation machine with speaker and microphone) and it would have cost roughly 50 cents to a dollar per unit. Morita alone refused, on the grounds that the device must have exactly one function.
→ The Walkman shipped as an unambiguous personal music player and defined a category; recording was added only much later, once people were familiar with the concept.
The American diner ran on customisation — how do you want your eggs, over easy, sunny side up, poached, scrambled, substitutions. The McDonald brothers stripped this back to a short fixed menu.
→ The win was partly speed, simplicity and supply chain, but Sutherland argues it was crucially about choice reduction: do you want a Big Mac or don't you?
Common mistakes
Justifying a feature by its marginal cost
'It costs almost nothing and it doubles the functionality' is precisely the argument Morita rejected. Cheap features that create ambiguity about the product's purpose are the most dangerous kind.
Assuming functionality maps linearly to value
Logically greater functionality should mean greater utility and greater value. Psychologically, more than one function means the customer does not know where to start.
Offering unlimited customisation
Infinite options do not delight; they paralyse and inflate the perceived price until the buyer cannot justify the purchase at all.
Is it for you?
Best for
Founders and product managers under pressure to add features to a product whose core proposition is still being learned by the market.
Not ideal for
Mature platforms and enterprise suites where buyers explicitly evaluate on breadth of capability and integration.
From the transcript
“Marita said you don't want to double the functionality of the device you want the device to have one function which it performs very well…”
“once it's got more than one function people don't know where where to start”
“I think Tesla's quite clever in that the choice architecture of Tesla's is just the right amount of choice”
From the episode
What most people miss about marketing
Rory Sutherland (Vice Chairman of Ogilvy UK, author)