Simple Equations Behind Interaction Design

1. Attention = Motion + Meaning

If something moves, we look at it.
But if it moves without reason, we get confused.

That’s the first design equation:

Attention = Motion + Meaning

A button that wiggles should say, “Hey, I’m clickable.”
A loading bar that fills should say, “I’m working on it.”
Every motion must carry a message — otherwise it’s just noise.

Design advice: When you animate, don’t decorate. Communicate. Motion is language.

2. Trust = Clarity ÷ Surprise

People trust what they understand.
But they also enjoy being surprised — just not too much.

That’s why we say:

Trust = Clarity ÷ Surprise

If clarity is low (the system hides what it’s doing), even a tiny surprise feels scary.
If clarity is high (users understand the logic), you can add a dash of magic.

Think of it like a playground slide — it’s fun because you know how it ends.

Design advice: Before you delight, explain. Every pleasant surprise rests on predictable ground.

3. Control = Options – Confusion

More options don’t always mean more control.
In fact, every new choice adds a little confusion.

So the next rule is:

Control = Options – Confusion

The best interfaces make users feel powerful without making them think too hard.
You don’t need a thousand knobs when one clear action does the job.

Design advice: Give users a clear path, then let them explore — never the other way around.

4. Satisfaction = Effort ÷ Reward

People judge experiences like they judge snacks — is the taste worth the effort?

That’s why we measure:

Satisfaction = Effort ÷ Reward

If something takes too much time, even a good result feels annoying.
But if it’s too easy, it feels shallow. The best designs strike balance: a small challenge, followed by a meaningful outcome.

Think of a puzzle game — it’s fun because you worked for it.

Design advice: Let users earn their success. Make every click feel like progress, not labor.

5. Memory = Emotion × Repetition

People forget features but remember how they felt.
That’s why habit-forming design isn’t about stickiness — it’s about emotional rhythm.

So:

Memory = Emotion × Repetition

If something makes you feel good once, you smile.
If it makes you feel good every time, you come back.

Designers who understand this don’t design screens — they design moments that echo.

Design advice: Consistency isn’t boring. It’s trust rehearsed over time.

Putting It All Together

Interaction design looks complex, but it’s really a set of emotional equations:

Equation What It Balances
Attention = Motion + Meaning How people notice things
Trust = Clarity ÷ Surprise How people feel safe exploring
Control = Options – Confusion How people make confident choices
Satisfaction = Effort ÷ Reward How people feel progress
Memory = Emotion × Repetition How people remember you

If you design with these in mind, your interface starts to behave like a good friend: clear, honest, and fun to talk to.