Behavioral Design:
Making People Predictably
Better

Kristen Berman

CEO & Co-founder, Irrational Labs

BEHAVIORAL SCIENCE

Foundation

The 3 Bs of Behavior Change

"People make decisions with lots of emotion. We are present bias. We follow social norms. But the good news is we do these things in predictable ways."

Motivation: Does the user want to do this? Are they actually thinking about the benefits?
Barriers: What logistical and cognitive friction prevents them from doing it?
Benefits: Are the benefits immediate or delayed? Immediate wins drive action today.

Case Studies

Real Impact from Behavioral Design

24%

less misinformation shared (TikTok)

53%

purchase rate increase (TytoCare quiz)

133%

conversion boost (Trunk Club)

TikTok: Slowing Down Sharing

Added unverified label + "Are you sure?" popup at share moment. Reduced misinformation shares by 24% by interrupting the hot state and making people reconsider.

TytoCare: Quiz Engagement

Instead of carousel benefits, asked medical behavior questions during signup. 53% of quiz completers purchased vs. 37% who didn't. Active engagement drives motivation.

FinTech Surprise

Budgeting feature had zero impact on spending despite being top user request. Behavioral diagnosis revealed too many steps. Defaults would work better.

Credit Karma

Helped increase auto-deposit setup by 18% through reducing cognitive load. Defaults and rules of thumb beat features that require active decisions.

Playbook

How to Apply Behavioral Design

Do a behavioral diagnosis: Map every step your user must take. If it's too many steps, the behavior won't stick.
Ask questions, not carousels: Get users actively thinking about benefits. Multiple-choice questions beat open text fields.
Reduce, don't add: To decrease a behavior (like sharing misinformation), add friction. To increase, remove it.
Time matters: Friction should interrupt hot states. Benefits must be immediate, not delayed.

Budgeting paradox

Users requested budgeting. The team almost built it. But 10K user test showed zero impact. Why? Too many cognitive steps. Design for what users actually do, not what they say.

Rules of thumb

Instead of "should I take Lyft today?", use a rule: "I take Lyft on weekends only." Simple heuristics stick. Complex decisions don't.

The Dark Side

Getting Incentives Right

You become what you measure. LendingClub incentivized conversions, which made Kristen almost a predatory lender.
Measure behavior, not vanity metrics. Behavior aligns better with customer outcomes than retention or DAU.
Extend the time horizon. Quarterly targets breed short-term exploitation. Annual targets align with customer good.

The LendingClub lesson

Incentive: $$ for 5-point conversion bump. Result: Kristen suggested predatory tactics. Legal team said no. She hit 4.5 points anyway. Almost sold her soul. Incentives drive behavior, yours AND your users'.

Contrarian

What Behavioral Science Actually Says

✗Give people features and they'll use themINSTEAD →✓ Test with real users first. Budgeting was top request but had zero impact. Ask, don't assume.

✗Lower friction always increases conversionINSTEAD →✓ Adding friction can boost conversion if it makes users think about benefits. Questions beat carousels.

✗Behavior change comes from mindset shiftsINSTEAD →✓ Behavior drives identity, not the reverse. You become a person who does things by actually doing them. Redesign environments, not attitudes.

✗Behavioral tactics are manipulativeINSTEAD →✓ The ethics depend entirely on your incentives. Set the right KPIs and behavioral science becomes pro-consumer alignment.

Based on Kristen Berman's episode on Lenny's Podcast. All ideas on this page are from the episode.Watch on YouTube Follow @bermster on X

GO DEEPER IN THE EPISODE

05:45 What are behavioral economics and behavioral design?06:50 The fintech budgeting experiment 10:46 What drives behavior change?11:35 Why increasing friction can sometimes increase conversion 13:51 How to ask the right questions for user engagement 16:09 How Kristen got her start in behavioral economics 18:10 The 3B model of behavior change 20:37 Cognitive barriers 22:02 The importance of building products with immediate benefits to the user 24:20 How exploitation can occur 26:45 How to set customer-friendly incentives 29:15 How Kristen reduced the sharing of misinformation on TikTok 31:58 Tips for researching and solving problems 35:36 The One Medical case study 38:31 Rules of thumb for improving flow 41:46 What is right-for-wrong?47:00 How to get started using behavioral design 49:33 The Behavioral Design Bootcamp 52:01 Lightning round!

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