Welcome to psychology in design. After all our discussions about empathy and understanding the user, you're probably not surprised to learn that psychology is a big deal in UX design. Nearly everything is designed to fit humans, from pants pockets to electric cars. But that wasn't always the case. Believe it or not, it took two world wars for designers to consider what we now call the human factor. The human factor describes the range of variables humans bring to their product interactions. Before World War I, the objective was to fit the human to the machine. When planes started being used in war, that changed. Suddenly, untrained soldiers had to learn how to fly. Aviation psychology was introduced, and an attempt was made to mold the machine to fit the human. Unfortunately, in the early 1900s, the technology just wasn't good enough yet. During World War II, the sheer number of men and women needed for the war effort made it impossible to choose specific people for specific tasks. Aviation design had to consider human factors. In this case, human factors were the pilots' varying skill levels. If we were robots, some computer genius could just program us to be expert fliers. But we're only human, and not everyone flying a warplane was an ace pilot. To account for this human factor, we had to adapt the plane to the pilot. And by World War II, we finally had the tech to do it. So, what are some of the human factors that inform design? Here's a few of the most common ones: impatience, limited memory, needing analogies, limited concentration, changes in need, needing motivation, prejudices, fears, making errors, and misjudgment. For an example of design that considers these factors, all you need to do is check your email. The business email shorthand TL;DR has really caught on in the last couple of years. It's an acronym you might find at the start of a very long email. A TL;DR is a short, succinct summary that only gives you the email highlights you really need to know, without any excess content. So, what does TL;DR stand for? Too long; didn't read. The email writer factors in the human tendencies of impatience, limited concentration, need for motivation, and limited memory. Not bad for four little letters. Here are psychological concepts that can help you design with the human factor in mind. Mental models are internal maps that allow humans to predict how something will work. When you face a door, your mental model tells you that the door can be opened. Once the door is opened, you'll be able to leave the room. The process of opening the door is expected to end with you being able to leave the room. A mental model breaks when you can't go through the open door because, for example, there's a solid brick wall behind it. The next psychological concept is feedback loops. Feedback loops refer to the outcome a user gets at the end of a process. For example, if you enter a dark room and flip a light switch, the room will either brighten, or it won't. Positive feedback would be the light coming on. While negative feedback would be nothing happening. The more positive feedback a user gets when completing the action, the more they will expect the outcome to be positive. The same is true with negative feedback. If your user takes an action, it's important that they get some kind of confirmation that the action worked or that it didn't. In spite of all the limitations the human factors puts on UX designers, it also gives us opportunities to create even better user experiences. Sometimes a well-known brand will revert their product packaging back to the original design in order to connect to a user sense of nostalgia. For example, a potato chip company might reissue its classic bag design from the '80s, or a century-old soda company might create replicas of bottles they used decades ago. In these cases, the designer uses nostalgia to connect with users, something they couldn't use to connect with robots. When UX designers turn limitations into opportunities, the human factor isn't so limiting after all. Pretty cool, right? Coming up, we'll go through some of the psychological principles that act on the user's subconscious as they interact with the product.