Module 3: Biases and mental models

How the user decides

Learning objectives: By the end of this module, you will be able to:

Foresee how the expectations the user brings from other products affect yours.
Evaluate when reducing options helps people decide and when it gets in the way.
Design the ending of an experience knowing it weighs more in memory than its duration suggests.

Estimated time: 1-1.5 hours

The user doesn't arrive at your product blank. They arrive with expectations formed across hundreds of other products, with limited patience for deciding, and with a memory that's going to play tricks on them about what they just went through. This module is about those three facts and how they shape every decision the person makes in front of your screen.

Here we step out, for the first time, of purely cognitive territory. One of the phenomena we'll look at, Jakob's law, is social at bottom: it has to do with what the person learned from collective behavior, not just from inside their own head. I'll flag it when we get there.

3.1. The restaurant analogy

Walking into a new product is like walking into a restaurant. Three things happen almost immediately, and each one is a different phenomenon:

First, you already know how a restaurant works before you sit down: you expect to be seated, to get a menu, to order and then pay. Nobody explains it to you; you learned it in every previous restaurant. That inherited expectation is Jakob's law: people spend most of their time on other products, so they expect yours to work in a similar way. Tradition: social psychology (you learned it from other people's behavior, you didn't work it out alone).

Second, if the menu has two hundred dishes, instead of feeling lucky you freeze. Too many options don't liberate: they weigh you down. That's choice overload.

Third, when you leave you don't remember the average of the meal. You remember the best bite and how it all ended: whether the check came fast, whether they said goodbye well. That's the peak-end rule.

One single moment, going out to eat, governed by three different phenomena. Let's take them one at a time.

3.2. Three design decisions, one per phenomenon

Step 1: respect the mental model before innovating (Jakob)

Before inventing a new pattern, look at how the products your user already uses every day solve it. If you're going to break the convention, let it be for a clear gain.

Its limit: following convention to the letter kills differentiation, and conventions change over time. Jakob is a guide for picking your battles, not an order to copy.

Step 2: reduce options where the person has no criteria; expand them where they do

Its limit: the choice overload effect is overstated. The famous jam study (Iyengar and Lepper, 2000) doesn't always replicate; a later meta-analysis (Scheibehenne and colleagues, 2010) found an average effect close to zero. It depends on the domain, on whether the person knows what they want, and on how the options are organized. Don't cut out of dogma.

Step 3: design the peak and the end, not just the average (peak-end)

Locate the most intense moment of the experience and the last one, and work them carefully. A poor ending ruins a good journey.

Its limit: the peak-end rule describes the memory of the experience, which can differ from how it was lived moment to moment. Optimizing only for memory can lead you to neglect the during. It also comes mostly from studies of affective and painful experiences; carrying it over to UX is reasonable, not a certainty.

Going deeper: the two gulfs (Norman)

Jakob's law is about what the user expects out of habit. Donald Norman's "gulfs" point at something deeper: the distance between what the person wants to do and what the system lets them do. Norman splits it in two. The gulf of execution is the distance between intention and action: "I want to do X, how is it done here?". In the restaurant: do I order at the table, go to the counter, raise my hand? The gulf of evaluation is the distance between what the system did and what the person manages to understand of it: "did it work?, what happened?". In the restaurant: did my order go through?, is it being prepared or did it get lost? A gulf is closed with good signifiers and good mapping (execution) and with good feedback (evaluation), and it opens when the system's model does not match the user's mental model.

Unlike Jakob's law, this is cognitive, not social: it does not come from what other people do, but from the person's own intention and interpretation.

Its limit: the gulfs are a frame for locating where the problem is (in the action or in the interpretation), not a measure of how big it is nor a recipe for closing it. They name the place; the size and the solution still have to be researched.

3.3. Case study: "GimnasioApp" (subscription)

GimnasioApp did almost everything right. Sign-up was a delight: two taps, first class booked on its own. For months, the app worked. And yet the reviews were lukewarm and word of mouth was negative. The team didn't get it: the daily experience was good.

The problem was in the ending. Cancelling the subscription required a phone call during business hours, listening to a retention offer and confirming three times. Even if the user only cancelled once, that was the last memory they took away, and the one they later told others about. By the peak-end rule, a hostile ending colors months of good experience.

The obvious fix is to let people cancel as easily as they subscribe. The uncomfortable one is a business matter: that difficult ending was put there on purpose, to retain. Here the research finding collides with a commercial incentive, and naming that tension is part of the job. We come back to this in the ethics module.

3.4. Application activity (15 minutes)

Pick a product or service you used for months and no longer use, or one you use today.

Remember its most intense moment (good or bad) and its ending: a cancellation, an error, a goodbye.
Ask yourself whether your overall memory looks more like the average of the experience or like that peak and that ending.

Suggested solution: almost always the overall memory is better explained by a peak and by the ending than by the average. If your memory of a service is bad despite mostly good use, suspect the ending: that's usually where the explanation is.

3.5. References

Nielsen, J. (2000). Designing web usability: The practice of simplicity. New Riders. (Jakob's law, formulated by Jakob Nielsen / Nielsen Norman Group.)
Norman, D. A. (2013). The Design of Everyday Things (revised and expanded ed.). Basic Books. (Originally 1988.)
Iyengar, S. S., & Lepper, M. R. (2000). When choice is demotivating: Can one desire too much of a good thing? Journal of Personality and Social Psychology, 79(6), 995–1006.
Scheibehenne, B., Greifeneder, R., & Todd, P. M. (2010). Can there ever be too much choice? A meta-analytic review of choice overload. Journal of Consumer Research, 37(3), 409–425.
Kahneman, D., Fredrickson, B. L., Schreiber, C. A., & Redelmeier, D. A. (1993). When more pain is preferred to less: Adding a better end. Psychological Science, 4(6), 401–405.

Additional material. From MIT's Introduction to Psychology (9.00SC): Thinking for judgment and decision making; Social Psychology I and Social Psychology II for the social root of Jakob's law.