Poor usability kills
“[…] usability really just means making sure that something works well: that a person of average (or even below average) ability and experience can use the thing—whether it’s a Web site, a fighter jet, or a revolving door—for its intended purpose without getting hopelessly frustrated.”
Steve Krug: Don’t Make Me Think
Usability is the practice of making a thing easy to use. This can be a website, an app on a phone, or software, but it can also be physical appliances and other machines.
Good usability not only ensures that the user can use the thing, but also that they don’t use the thing in a detrimental way. An example of this could be a railroad traffic control light, which tells the train driver to either stop or continue. The signal has two lights, either one or both of which can be turned on.
The signal to stop will probably be the most important one, as this is likely to mean that the track ahead is blocked. It is therefore logical to make the signal to stop the hardest one to miss, and set it to be when two lights are on. The signal to continue would then be to have only one light on.
The problem here might not be obvious, but it is very important: If one of the lights fail, the signal to stop will look like a signal to continue.
The solution is to make the signal to stop one light, and the signal to continue two lights. If the conductor sees anything other than two lights, they will stop. This may sometimes cause unnecessary delays, but delays are preferable to derailed trains.
Historically, usability in physical devices is much more ingrained in their design because physical devices can accidentally kill people. As more and more physical machine and processes become controlled by software, software engineers and designers are increasingly getting the same power as mechanical engineers to inadvertently kill people through poor usability (or maybe give a child in a hospital 38 times the correct dose of medicine).
Most days, poor usability on websites will not kill people. It may, however, result in lost customers, wasted time, errors, decreased employee satisfaction, and as Web Content Accessibility Guidelines becomes enscrined in law, fines.
Assumptions about users
There are more than 1.5 billion websites. This means that no person will ever visit most websites even once, much less twice. For this reason, most website owners can’t many any assumption about their users, perhaps other than that they know how to click a link.
Some websites have repeat visitors. This is especially true for social media sites and other services that are frequently used. By definition of their market penetration, Facebook, LinkedIn, Twitter, Amazon, and Google will almost exclusively have repeat users. These websites can make some assumptions about their repeat users. Incidentally, the sign-up screens of these websites are often much more minimalistic and supportive than their regular interfaces.
Another type of website is software internal to corporations. Software is increasingly written to be used through the employee’s browser, and can usually not be accessed directly throug the Internet. Because this software is used frequently by people trained in the specific area, these websites can make significant assumptions about their users.
Usability always matters
Regardless of whether a user visits a website only once in their lifetime, many times every week, or constantly during their workday, usability is always important.
For one-time users, usability ensures that the user can be on their way quickly.
For repeat users, usability ensures that the user does not grow weary and leaves for a competitor.
For internal corporate users, usability ensures the user’s work is done quickly and without errors.
Users must never feel satisfied
If a website is difficult to use, the user will often become dissatisfied, and will start filling up inboxed with questions and complaints. This is obviously a bad thing.
It would stand to reason that the result of good usability is satisfied users and praise. Regrettably, this is not the case. Truly good usability makes the user’s interactions and choices invisible to the user. The user must not think, “This is obviously where I need to enter my search.” Instead, the user must enter their search without thinking about where to do so, or even that they want to do it. Good usability makes every task intuitive to the user.