The Lean Product Process will guide you through the critical thinking steps required to achieve product-market fit. In the next chapter, I begin describing the details of the process, but before I do, I want to share an important high-level concept: separating problem space from solution space. I have been discussing this concept in my talks for years and am glad to see those terms used more frequently these days.
Any product that you actually build exists in solution space, as do any product designs that you create—such as mockups, wireframes, or prototypes. Solution space includes any product or representation of a product that is used by or intended for use by a customer. It is the opposite of a blank slate. When you build a product, you have chosen a specific implementation. Whether you've done so explicitly or not, you've determined how the product looks, what it does, and how it works.
In contrast, there is no product or design that exists in problem space. Instead, problem space is where all the customer needs that you'd like your product to deliver live. You shouldn't interpret the word “needs” too narrowly: Whether it's a customer pain point, a desire, a job to be done, or a user story, it lives in problem space.
My favorite story to illustrate the concept of problem space versus solution space is the space pen. When NASA was preparing to send astronauts into space, they knew that ballpoint pens would not work ...