A major limitation of A/B tests is that because it’s difficult to come up with holistic measures of success, the results tend to be pretty narrow. Perhaps that’s okay if your definition of success is increased profit. Making more money is easy to measure. But if your definition of success is harder to measure (e.g., there’s less hate speech on your platform), A/B tests might be much harder to conduct. The ease with which A/B tests can run, and the difficulty of measuring meaningful things, can lead designers to overlook the importance of meaningful things. A good designer will resist this path of least resistance, focusing on the outcomes that matter to a design, independent of what tools make easy.

This means that every prototype has a single reason for being: to help you make decisions. You don’t make a prototype in the hopes that you’ll turn it into the final implemented solution. You make it to acquire knowledge, and then discard it, using that knowledge to make another better prototype.Because the purpose of a prototype is to acquire knowledge, before you make a prototype, you need to be very clear on what knowledge you want from the prototype and how you’re going to get it. That way, you can focus your prototype on specifying only the details that help you get that knowledge, leaving all of the other details to be figured out later. Let’s walk through an example. Imagine you’re working with a community of assisted living residents who want the ability to easily order a pizza without having to remember a phone number, make a phone call, or share an address. You have an idea for a smart watch application that lets you order delivery pizza with a single tap. You have some design questions about it. Each of these design questions demands a different prototype:

On the other hand, there are some design principles that one might use to make more absolute judgements of “good” design. Let’s start with some common, but vague principles, that are not particularly useful:Intuitive. Human beings are not born with much innate knowledge. What people mean when they use this word is that someone can infer from the information in a design what the purpose or intent of something is, based on all of the prior knowledge they’ve acquired in their life, including encounters with a long history of user interface conventions and domain concepts. That is not “intuitive,” but rather, closely mapped to someone’s knowledge.User-friendly. This is another imprecise phrase. What does it mean to be “friendly” with a user? Nice? Supportive? Helpful? This phrase suggests a lot without meaning a lot, and does not facilitate precise design critique.

Some design scholars have questioned whether focusing on people and activities is enough to account for what really matters, encouraging designers to consider human values77 Friedman, B., & Hendry, D. G. (2019). Value sensitive design: Shaping technology with moral imagination. MIT Press. . For example, instead of viewing a pizza delivery app as a way to get pizza faster and more easily, we might view it as a way of supporting the independence of elderly who do not have the mobility to pick up a pizza on their own. Or, perhaps more darkly, instead of viewing TSA screening at an airport a way of identifying potential terrorists, we consider it through the value of power, as the screening process had more to do with maintaining political power in times of fear than it did with actually preventing terrorism. This shift in framing can enable designers to better consider the values of design stakeholders through their design process, and identify people they may not have designed for otherwise (e.g., people who are house bound because of injury, or politicians).

One critique of all of these approaches, however, is that no design, no matter how universal, will equally serve everyone.

One critique of human-centered design is that it narrowly focuses on people and their needs rather than a systems-level view of the activities that people engage in, and the multiple people and systems involved in those activities. For example, consider the activity of driving a bus: it’s not just the driver that matters, but the dispatchers that communicate information to drivers, the other drivers on the road, and even the riders occasionally.