We all think that we see a thing as it is when we look at it. But this is not true. We see things how we look at them.
I just realized this while looking at the patterns on the dining table in my kitchen:
When I look at this image for ascending line patterns, I see columns. When I look for descending line patterns, I see those instead. When I look for the V-shape formed by both, I see those lines; when I look for the A-shape, I see them as columns. When I look for both separately, I see both but with less focus—likely because my brain shifts from one to another rapidly.
Our brains only see what they look for.
My cat, Hureyre, doesn't see this at all. He only sees the piece of meat or butter I put on the table. He doesn't see text on paper or patterns on bed sheets. He doesn't notice the different clothes I wear. He has only a few interests: moving objects, noise-making things, and things that could be prey, a friend, or a danger.
His cat brain just works this way. This interest can be extended through association. For example, I taught him the question "Acıktın mı?" (Are you hungry?), and he recognizes it. I trained him to respond affirmatively because he knows food follows. But his focus only extends so far, always depending on his basic desires.
Humans work the same way. We need developed curiosity to care about certain things. My mom doesn't look into a car's design or performance—she just wants to get from point A to B. My brother, however, knows many brands and how they perform differently because he is interested in the joy of driving.
When I see a website or an app, I see many exciting details. When I show them to non-designers, they often can't say more than "it looks nice" or "the colors are good." They don't care about the details that I recognize separately. Instead, they look for the general feel they get from the design.
A viewer on a landing page looks for things that interest them: "What is this about?", "What are the benefits?", or "How does this make me feel?" The brain rapidly shifts focus. If they stay within one focus and keep seeing related things, they remain engaged more easily.
Everyone looks for specific things and ignores the rest, also at varying levels. Some interests can be 1/10 importance while some are 9/10. Catching a viewer's attention requires knowing how that attention flows. A designer’s eye must constantly look for the same things the visitor seeks.
Because of this, identifying all the things the user looks for — simultaneously and effectively — becomes the essential skill a designer must master to build products that truly achieve success.
Further Reading / Relevant Concepts: If you're interested in the psychology behind this, these ideas are also explored in Gestalt Principles:
Multistability: The mind switches between different interpretations of the same image.
Continuity: Our eyes naturally follow the smoothest path or line.
Closure: The brain fills in gaps to perceive a complete shape.