Yet sometimes even this simple task is beyond us.

Without a sign on the door saying whether we should push or pull, even a door can be a challenge. Often, it’s not evident whether to push or pull. If the door is made of glass, has no handle, and the hinges aren’t easy to locate, we can find ourselves pushing a door in vain on the side of the hinges.

Imagine you’re a product designer designing a new washing machine. Although it’s a common household appliance, your washing machine will need new features so it stands out from the competition. But for your users to be able to understand these new, unfamiliar features, you’ll have to take their psychology into consideration.

Users engage with a product on three different psychological levels.

First comes the visceral level, which corresponds to the unconscious behaviors we do without thinking, like breathing and digesting.

Next comes the behavioral level. This level includes the quick reflexes we use when we play sports, like catching a ball, or short-timed responses to actions, like pulling our hand away from a fire. These are conscious responses, but don’t allow us a lot of time to think about them.

Finally, the reflective level is the realm of conscious, higher cognitive functions where we perform complex planning and problem solving.

In the old flight control model, the button to increase or decrease velocity looked the same as the button to increase or decrease the angle of descent or ascent. This led to many pilots getting confused; although it was the pilots who were making the mistakes by confusing the buttons, it was the design error of making the buttons confusing (the root cause) that led to the mistakes in the first place.

By changing the flight controls’ appearance, designers were, paradoxically, able to decrease the chances of “human error.”

There are cultural constraints, which are the product of shared beliefs. An example of this is the international screw standard. We all know to turn screws one way to tighten them and another to loosen. We take it for granted, but it’s this community-wide knowledge which makes the screwdriver so easy to use!

Constraints can also help remind people about important uses for the device that they may have forgotten. Imagine you’re working on a document on the computer. You work on it for many hours, but close it down without saving – big mistake!

Good design provides answers to the user’s questions and clarifies confusions. To do so, the device needs to communicate with users to guide them through using the device. It’s this feedback – in the form of signs, sounds and vibrations – that help the users understand the device.

Great, human-centered design isn’t enough to make a successful product on its own. For a product to be profitable, designers needs to work with other business departments.

This is the dilemma: for a product to succeed, both departments need to be in accord with one another. The product needs to be of high enough quality for the designer and profitable enough for the marketers.