Design me a chair. What do you need or want from a chair? What is the average user of a chair? Size? Needs? Wants? Comfort? What is the maximum range of variety in these users? What can I design to fulfill most of their needs? This is user-centered design.

Firstly, we are human. This means that we possess an amazingly complex library of schemas that help us navigate the world. We are cognitive beings. The magic number in cognition is 7. We can hold in our heads 7 bits of information. As a classic example, our telephone numbers (here in the US) is seven digits long. Yes, we have more digits in other numbers, which brings up grouping. We group information (as psychology calls it “chunking”) so that we can remember more of it and more easily. Design knowledge alert: this relates to Gestalt—grouping, proximity, closure. Our brains want to group things by patterns we already know. Typography is helping us group all the time. We can’t take in whole paragraphs without a few periods, commas and capitals in the process.

Technology has its own way of easing the process through skeuomorphs. These things are the vestigial remnants of technology we already know and putting them in a new context. A camera phone doesn’t have to sound like the clicking of an aperture, but it does because it’s an indication we’re used to.

Physically, we are human. In fact, we are designing for humans more and more these days with the use of mobile devices. Phones, iPads, Androids, etc. force us to use our meaty fingers to make selections. (FYI: button size should be at least 40×40 pixels.) We need to think about people’s natural movements; how their hand dominance will affect the way they interact with something.

Blindness doesn’t inhibit you as it once did. Color-blindness is, in fact, more common than you think (10% of us) and we need to design with more than just color-indication if we want to keep our apps user friendly. Check out this website, so you can see how your screen looks to them. I never thought about what if a blind person wanted to look at this site. I haven’t labeled my pictures well enough for their “alt tag” readers can accurately portray what has been depicted. I can’t imagine any blind people have wanted to look at my designs, but I like the idea that if they do, I’m ready with something for them, too.

I keep thinking of that scene where Amelie (in the movie by the same name), where she leads a blind man down the street, just for a little while describing the idiosyncrasies of life as they pass. What a lovely thing to do for someone else.