Ryan Singer: Products Are Functions

The user starts in some circumstance x. Whatever product or solution they apply is a function f(). Applying the product to that circumstance f(x) produces a result: y.

The functional view bakes in causality. Customers make decisions in situations to achieve outcomes, rather than purely based on likes and dislikes. This framework forces you to think about what happens before and after they use the product.

Most designers set requirements for f() by describing what f() should be, which is a circularity. To be useful, requirements should be defined independent of f() as tests for fitness.

Designers often debate what is "good" in the absolute. As a result, fashion and personal preferences influence the solution more than casuality and context. Finding empirical values for x and y enables you to consider what needs to happen step by step to produce the right specific outcome, thus guiding you to a unique solution tailored to the probl... See more

Products are easier to reason about when you think of them as functions. They transform an input situation into an output situation.This lets you describe what the product does as a transformation of the user's circumstance instead of a bundle of features.

The product designer's task is to create a new f(). The designer doesn't get to define x: that's empirical. And they don't get to dictate y either. A given y is only a worthwhile target if it's worth paying for in the eyes of the user — also empirical. That means x and y are requirements for f(). They are fixed, f() is variable.