User interface design has to do with both the outer layer of a design and the placement of elements in the design, whether it be a website or an app. In simple terms, UI design refers to everything that users can see. However, the more important meaning involves the usability of a design. Just as with a street sign, if the design doesn’t provide clarity, then confusion can occur and scare users away, often permanently.

Of course, talking about the usability gets messy when it comes to terms. Many argue about the actual definition of labels such as UI and UX (user experience), and, really, it’s kind of a moot point here. After all, the “prettiness” and other visual aspects (UI) also have much to do with the usability side of design (UX), and this is why the terms UI and UX (user experience) are often used interchangeably, or at least why UX is more of an umbrella term under which UI falls and somewhat crosses. Because, really, both have to work together to really make a design stellar.

I like how Marci Ikeler puts it in a Quora forum on the difference between UX and UI designers: “Generally, what they [the company placing an ad] mean is: the UI/UX designer is a person who is responsible for strategizing, organizing, and executing an interface that accomplishes that company’s business goals.”

As a UI designer, you should definitely know the common – and not so common – mistakes made on various designs so that you can better help your client meet goals. If you know what to keep in mind while designing, you’ll be much more likely to create a website that matches your client’s description of “easy to use but makes a huge impression and leaves viewers with the right impression of our business so they buy lots of our stuff, forever and ever.” And, if your client insists on including any of the UI design mistakes listed below, you can make a valid argument for refusing…politely of course.