Not everyone uses a mouse to browse the internet. If you’re reading this post on a smartphone, this is obvious! What’s also worth pointing out is that there are other forms of input that people use to get things done. With these forms of input comes the need for focus styles.
People are complicated. We don’t necessarily perform the same behaviors consistently, nor do we always make decisions that make sense from an outsider’s perspective. Sometimes we even do something just to… do something. We get bored easily: tinkering, poking, and prodding things to customize them to better suit our needs, regardless of their original intent.
People are also mortal. We can get sick and injured. Sometimes both at once. Sometimes it’s for a little while, sometimes it’s permanent. Regardless, it means that sometimes we’re unable to do things we want or need to do in the way we’re used to.
People also live in the world. Sometimes we’re put into an environment where external factors conspire to prevent us from doing something the way that we’re accustomed to doing it. Ever been stuck at your parents’ house during the holidays and had to use their ancient-yet-still-serviceable desktop computer? It’s like that.