Interaction design is about shaping behavior—about creating a representational dialogue between a person and technology. An interaction designer thinks mostly about people and works to craft an interface on top of technology to help a person achieve their goals. The secret ingredient for an interaction designer is empathy with a specific person: feeling what it's like to be in the shoes of another person who will emotionally benefit from the design. This specific empathy is gained by watching that person work or play, by spending time with them, and by gaining knowledge of their behavior. This helps a designer reframe the design opportunity and structure a solution that will make sense for whomever it is intended to help.

The input for an interaction designer includes existing behavioral patterns, system and resource constraints, and both understanding with and empathy for a given person. The constraints placed on an interaction designer are derived from observational research and often from the creative process itself. The output for an interaction designer is typically some specification for design: A designer creates a diagram, sketch, or blueprint of his or her vision of the future. More important, a designer creates a convincing narrative of why their design is the right thing to be built; this story often shows how a design improves an existing situation.

Product management is about building and shipping the right product to the right people at the right time. It's about finding market opportunity, understanding product/person fit and product/market fit, and shaping a product that can be built and shipped quickly and efficiently. A product manager sits at the hub of a set of disciplinary spokes and works to align various constituents around a set of features, functions, and goals. The secret ingredient for a product manager is broad-based empathy: feeling what it's like to be in the shoes of a community of people who will engage with the design. This broad form of empathy is gained by absorbing market signals from related communities of people. This helps a product manager identify the right thing to build and the right time to build it in order to deliver the most value to the largest group of potential product users.

The input for a product manager includes existing technical capabilities, a rich understanding of the business and market goals, and an awareness of broad patterns of competitive product use. The constraints placed on a product manager are the resources available to actually design, build, and market the product—the team that is going to work on building the product. The output for a product manager is their product roadmap and, more important, a collaborative enthusiasm for that roadmap. Fundamentally, a product manager must recruit others to champion their product vision because they typically have no direct management influence over individual contributors. They are the glue that holds the product together.

Though the two roles are distinct, they have a large area of overlap. Both disciplines care about people and look to human behavior to understand what to build. Both disciplines care about technology and are tasked with making it easier for people to achieve their goals. And both disciplines are storytellers by necessity: Designers and product managers have neither carrot nor stick and must communicate and evangelize for a vision of the future that does not yet exist.

There is one major difference in the roles. Design is strategically optimistic, as it sees only potential. This optimism often means ignoring or suspending the reality of functional constraints—such as the constraint of human resources—in order to challenge existing or conservative ways of thinking. A designer may say something like, "If we want to achieve this vision, we'll hire the people who can build it." Product management is strategically tactical, as it is firmly planted in the reality of human resource constraints. A product manager must say, "I have these people available to help achieve this vision. Can they build this product? If not, how should I change the product to still achieve my goals?"

We are experiencing a broad acceptance of startup culture, where small groups of people can envision and produce an entire business with little to no organizational overhead. In a startup, people play multiple roles and take on activities that force a blending of roles and responsibilities. A merging of interaction design and product management takes place at many of these small companies, where the product team is the design team. In these environments, a shift from interaction design to product management is a natural evolution of roles and skill sets, but for designers looking to embrace this type of role, it becomes imperative that they expand their perspective to understand the vague idea of "the market." This is a widening of purview. The fit between a product and the market depends on the familiarity of competitive products and product accessories, the strategy for pricing and marketing the product, and the technological feasibility of building, distributing, and maintaining the product. Product/market fit generally takes and offers a macro view of the world, and prepares you for concepts and strategies. It's about understanding what consumers, broadly, want, and what the market, broadly, will bear.

Irrespective of your title, you will be highly successful and extraordinarily employable if you can simultaneously drive specific empathy and broad empathy: if you can gather signals from individuals and from a market, and synthesize those signals into a compelling—and achievable—vision of the future.