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Digital psychology, in one place.

50 principles of how people notice, interpret, decide and remember, and how the presentation of a price changes what it feels like to pay. Each entry has the study behind it and the ways I have used it in a product, a page or a campaign.

Built on the structure of Digital Psychology by Daniel Stefanovic, the coverage of the growth.design cheat sheet, and the tactics at Kolenda.io. Everything here is written fresh; studies are cited by author and year.

Attention

How people notice and filter what you put in front of them.

001AnchoringThe first number people see becomes the reference point for every number after it.002Hick's LawThe more options on screen, the longer it takes to choose, and the more people choose nothing.003Von Restorff EffectThe item that looks different is the item people notice and remember.004Visual HierarchyPeople read a page in the order its visual weight tells them to.005Cognitive LoadEvery element on screen costs attention, and attention runs out.006Progressive DisclosureShow the simple version first and reveal complexity only when it is asked for.007Fitts's LawBig targets that are close are fast to hit. Small targets that are far away get missed.008Banner BlindnessPeople stop seeing anything that looks like an ad or a thing they have seen before.009PrimingWhat people see first shapes how they read what comes next.010FramingThe same fact lands differently depending on how it is worded.011Decoy EffectAdd an option nobody should pick and the option beside it starts to look obvious.012Centre-Stage EffectIn a row of options, people gravitate to the one in the middle.

Meaning

How people interpret what they see and decide whether to trust it.

013Social ProofWhen people are unsure, they do what they see others doing.014ScarcityThings that are running out feel more valuable than things that are not.015ReciprocityGive something first and people feel obliged to give something back.016Curiosity GapPeople are pulled to close the gap between what they know and what they want to know.017Authority BiasPeople give more weight to a claim when it comes from someone who looks qualified.018Halo EffectOne good impression colours every judgement that follows.019Mere Exposure EffectPeople come to prefer things simply because they have seen them before.020Aesthetic-Usability EffectThings that look good are assumed to work well.021Singularity EffectOne named person moves people more than a statistic about thousands.022Mental ModelsPeople arrive with an idea of how your product works, and they judge it against that idea.023Noble Edge EffectPeople prefer to buy from businesses that seem to do some good.

Decision

What tips people from considering to acting, and keeps them acting.

024Commitment and ConsistencyOnce people have taken a small step, they want their next steps to match it.025Loss AversionLosing something hurts about twice as much as gaining the same thing feels good.026Variable RewardsUnpredictable rewards hold attention far longer than predictable ones.027TriggersBehaviour happens when motivation, ability and a prompt line up at the same moment.028Default BiasWhatever is pre-selected is what most people end up with.029Sunk Cost EffectThe more people have already put in, the less willing they are to walk away.030Goal Gradient EffectPeople speed up as they get closer to the finish.031Labour IllusionPeople value results more when they can see the work behind them.032ReactancePush people and they push back.033IKEA EffectPeople value what they helped make, even a little, far above what was handed to them.034Endowment EffectOnce something feels like yours, you want more to give it up than you would pay to get it.035Fresh Start EffectNew beginnings make people more willing to act on their intentions.036Spark EffectWhen the first step is tiny, people take it.037Hyperbolic DiscountingA smaller reward now beats a larger reward later.

Memory

What people keep after the session ends, and what brings them back.

038Need to CompleteUnfinished tasks stay in mind until they are done.039Peak-End RulePeople remember an experience by its best or worst moment and by how it ended.040ChunkingInformation in small groups is understood and remembered; information in a stream is not.041DelightersSmall, unexpected pleasures are remembered long after the features are forgotten.042Serial Position EffectPeople remember the first and last items in a list and forget the middle.043Recognition Over RecallIt is far easier to recognise something than to remember it from nothing.044Storytelling EffectFacts inside a story are remembered. Facts in a list are not.045Picture Superiority EffectPeople remember what they saw far better than what they read.046Aha MomentThe instant a new user first sees the value is the instant they decide to stay.

Pricing

How the presentation of a number changes what it feels like to pay.

047Charm PricingA price ending in 9 feels meaningfully lower than the round number above it.048Currency Symbol and Font SizeA price shown small, without a currency symbol, feels smaller.049Durations Over DatesA deadline expressed as a duration feels sooner than the same deadline as a date.050Partitioned and Bundled PricingSplitting a price into parts can make it feel smaller. Bundling can make it feel simpler.

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