Energy vs. hearts.

Last week, Duolingo announced a major shift: they’re replacing their long-standing hearts system with a new “energy” mechanic. The company frames this as a way to make learning more motivating by focusing on rewarding correct answers rather than punishing mistakes.

But after spending 48 hours thinking about this change and analyzing reactions across the internet, I’ve come to see it as something far more nuanced: a masterclass in behavioral psychology that serves both users and Duolingo’s bottom line in fascinating ways.

What’s actually changing

Under the old hearts system, users started with five hearts and lost one for each mistake. When all hearts were depleted, you couldn’t continue learning until you either waited (hearts regenerated over time), watched ads, practiced old content to earn hearts back, or paid for premium.

The new energy system gives users 25 energy units. Each lesson costs one unit to start, and mistakes also cost energy. The key difference? Users can earn bonus energy at random intervals when answering correctly.

As Moses Wayne, a senior staff engineer at Duolingo, explains to The Verge: “We feel like this is a way that we can motivate you to focus on things you’re getting right rather than penalizing for the things that you’re making mistakes on.”

It sounds positive on the surface. But there’s much more happening under the hood.

The psychological switch: from loss to expenditure

The hearts system was built on loss aversion (our tendency to feel losses more intensely than equivalent gains). Users would desperately try to avoid mistakes to keep their hearts. In psychological terms, this creates anxiety that can inhibit learning, especially for a complex skill like language acquisition.

The energy system cleverly shifts the frame from “losing hearts through mistakes” to “spending energy to learn.” This slight repositioning transforms the psychological experience. Instead of punishment, it’s now an investment.

But here’s where it gets particularly interesting, and perhaps concerning.

Variable rewards: the slot machine mechanism

The new system incorporates one of the most powerful psychological techniques in existence: variable reward schedules, or what behavioral scientists call “intermittent reinforcement.”

When completing lessons, users now receive random bonus energy for consecutive correct answers. This unpredictability is the same mechanism that makes slot machines so addictive. As behavioral psychologist B.F. Skinner discovered decades ago, unpredictable rewards create stronger habit loops than predictable ones.

The uncertain nature of “when will I get bonus energy?” creates a dopamine response that keeps users engaged far longer than the more predictable hearts system. One psychology research article noted that “variable ratio schedules have two benefits: They result in the most instances of the behavior than any of the other schedules… and they result in behaviors that are ‘hard to extinguish,” meaning the behavior persists even when rewards decrease.

Duolingo isn’t the first app to use this technique. It’s everywhere in modern digital products, from social media (random likes triggering dopamine) to games (loot boxes with variable rewards). What’s notable is how Duolingo is implementing it in an educational context.

The inverse energy model: Finch vs. Duolingo

To understand what makes Duolingo’s approach unique, it’s worth comparing it to another popular app that uses an energy system: Finch.

In Finch, a self-care app with a virtual pet, users earn energy by completing wellness tasks. As one reviewer describes it: “My effort gives [my pet] energy, but my lack of effort takes none away.” The energy you earn through self-care allows your pet to go on adventures and grow.

Duolingo takes the inverse approach, i.e. you spend energy to engage with the product. This fundamental difference reveals contrasting philosophies:

• Finch’s model: Do real-world activities → earn in-app energy → enjoy rewards
• Duolingo’s model: Spend in-app energy → engage with content → occasionally get energy back

While both use similar terminology, the direction of energy flow completely changes the behavioral dynamics. One rewards external action; the other creates a closed loop that keeps users in the app.

The business of artificial scarcity

Let’s not overlook the monetization angle. Super Duolingo subscribers get unlimited energy, just as they previously got unlimited hearts. The new system maintains the same fundamental constraint: free users eventually hit a wall where they need to either wait, work harder, or pay up.

What the energy system might do more effectively is increase the perceived value of the premium subscription. By creating a more engaging core loop with the variable rewards, users may be more likely to convert when they hit energy limits.

The strategy is brilliant, if perhaps ethically complex. By transforming a negative experience (punishment for mistakes) into a more positive ne (spending a resource with occasional bonuses), Duolingo has maintained its monetization constraints while making them feel less punitive.

Critics of the heart system have long pointed out that unlimited hearts are one of the main selling points of Duolingo’s premium tier, suggesting the constraint exists primarily to drive conversions rather than improve learning. The energy system continues this pattern, just with more sophisticated psychological underpinnings.

The learning science question

The most important question is whether this change actually improves learning outcomes.

Duolingo claims the energy system helps users “get through more lessons,” as the data shows users can do more with the new system. But completing more lessons doesn’t necessarily mean better language acquisition.

Language learning requires making mistakes. It’s a fundamental part of the process. The old heart system discouraged risk-taking by heavily penalizing errors, potentially leading users to stick with easier content where they wouldn’t lose hearts.

The energy system might ease this anxiety somewhat — making a mistake costs the same as starting a new lesson. But the fundamental constraint remains: you still have a limited resource that depletes when you make errors.

A truly learning-optimized approach might involve no penalties for mistakes at all, focusing instead on spaced repetition, comprehensible input, and other evidence-based language acquisition methods. But such an approach might not drive the same level of engagement or monetization.

Users vs. learners

This tension highlights a key challenge for educational technology: the gap between what creates engaged users and what creates successful learners.

The techniques that make an app sticky (intermittent reinforcement, streaks, gamification) don’t always align with optimal learning science. In fact, they can sometimes work against it by encouraging shallow engagement over deep processing.

Duolingo has always walked this line, using game mechanics to keep people engaged with language learning when they might otherwise quit. The energy system represents an evolution of this approach, using more sophisticated behavioral psychology to maintain the same fundamental constraints while making them feel better.

The verdict: clever design for multiple objectives

After analyzing this change from multiple angles, I’m left impressed by its cleverness while somewhat ambivalent about its implications.

The energy system:

• Creates a more positive psychological framing than hearts
• Implements powerful variable rewards that increase engagement
• Maintains the same fundamental monetization pressure
• Potentially allows for more mistakes, which is better for learning
• Uses randomness to create stronger habit loops

It’s a change that serves both user experience and business goals, likely increasing both engagement and conversion to premium. Whether it truly serves learning outcomes remains to be seen, though it’s probably at least marginally better than the hearts system in this regard.

What fascinates me most is how this change reveals the sophistication of behavioral design in today’s digital products. What looks like a simple mechanic change is actually a carefully engineered system to shape behavior through psychological principles.

The next time you find yourself compulsively swiping for another lesson, hoping for that bonus energy to drop, remember that this feeling isn’t accidental… it’s by design.

And while I appreciate the brilliance of that design, I find myself wishing more of this psychological ingenuity was directed toward optimizing learning outcomes rather than engagement metrics. Perhaps that’s the next frontier for language learning apps: finding ways to make evidence-based learning as addictive as a slot machine.

Sam Liberty is a gamification expert, applied game designer, and consultant. His clients include The World Bank, Click Therapeutics, and DARPA. He teaches game design at Northeastern University. He is the former Lead Game Designer at Sidekick Health.

Duolingo’s small UI switch that changes everything was originally published in UX Collective on Medium, where people are continuing the conversation by highlighting and responding to this story.