By Guillermo Tena

Every interface tells a story, not just through visuals but through how it makes people feel over time. Every color, animation, or layout tweak sends a signal to the brain. Sometimes that signal is deliberate, other times it’s subtle enough that users barely register it until something feels different.
According to the Nielsen Norman Group, visual perception plays a key role in how users process these cues. Sometimes, the signal is deliberate; other times, it’s subtle enough that users barely register it until something feels different.

When users build habits around your product, those small changes can feel much larger than they are. That’s why great design is never only about how things work. It’s about how they evolve. And mastering that evolution means understanding a concept from psychology that quietly shapes the success or failure of digital products: the Just Noticeable Difference, or JND.

What the Just Noticeable Difference Really Means

In psychology, the Just Noticeable Difference is the smallest change in a stimulus that a person can detect about half the time. In design and product terms, it translates to a crucial question.

“How much can I change before users start to notice and possibly resist that change?”

Every product update lives somewhere along that threshold. Staying below it allows users to adapt naturally, while pushing beyond it risks triggering resistance before they see the value.

The goal isn’t to avoid change. It’s to orchestrate it, to make it feel intentional, consistent, and aligned with the user’s expectations.

The Psychology of Perception and Why It Matters in UX

To manage this balance, it helps to understand how people perceive change. Psychologists describe three perception thresholds.

• Absolute Threshold (Minimum): the faintest signal that can be detected, such as the dimmest glow of a screen.
• Absolute Threshold (Maximum): the point where input becomes overwhelming, too bright, too fast, or too different.
• Differential Threshold (JND): the smallest difference a person can perceive between two experiences, the moment something feels off even if it’s hard to explain why.

When a company rebrands, launches a new app, or redesigns an interface, it operates within these thresholds. The closer the change stays to the user’s comfort zone, the smoother the adoption. Ignore that balance, and what was meant to be evolutionary can suddenly feel disruptive.

BBVA: When Change Crosses the Line

A clear example of this balance can be found in the experience of BBVA, once recognized for having one of the most intuitive and trusted banking apps in Latin America and Spain.

For years, BBVA’s digital experience stood out for its clarity and consistency. Users built habits around it. They trusted it. Then came a complete redesign. Without gradual onboarding or clear communication, the update was introduced all at once, and that’s where things started to break.

The new interface was well-designed, modern, and aligned with BBVA’s global vision. But perception told a different story. Because everything changed simultaneously, users felt disoriented.

“Where did everything go?”
“Why does this feel harder?”
“Can I still do what I used to?”

The redesign crossed the JND, not visually but emotionally. BBVA didn’t just change the interface, it disrupted trust.

This isn’t a story about bad design. It’s a reminder that even good design fails if perception isn’t managed carefully.

Managing Change Without Losing Users

That brings us to a question every product and UX team eventually faces. How do you evolve without alienating your audience?

We often see how this balance determines whether users stay engaged or drift away. Successful teams understand that users don’t simply adapt to products, they adapt to routines. Breaking those routines takes care, timing, and strategy.

Here are five principles to guide that process.

Each of these principles builds on the same idea. Users don’t resist change because they dislike progress. They resist it because they lose familiarity.

What Smart Brands Get Right

Some of the most recognizable brands have mastered this balance. Spotify, for instance, continuously refines its interface but never in a way that feels like starting over. Updates are gradual, guided, and framed by what’s familiar.
Coca-Cola has modernized its image for more than a century, yet the essence, the red, the script, the curve, remains untouched.

These brands understand that perception is part of design. They evolve within the user’s comfort zone, introducing change so naturally that it feels expected rather than imposed.

Great Design Is Change You Don’t Notice

In the end, design isn’t only about what you see. It’s also about what you don’t.
The smooth transitions between versions, the subtle cues that preserve trust, and the way new features feel instantly intuitive, that’s the art of controlled evolution.

Real innovation isn’t about surprising users. It’s about earning the right to change their habits one detail at a time.

The best brands don’t just build better products. They build better transitions, guiding users from what’s familiar to what’s next without losing them along the way.

Let me know in the comments. I’d love to hear how your team manages change, perception, and trust.