An idea that lives only in your head cannot be tested, shared, improved, or evaluated by anyone else. A prototype — even a rough one — transforms an idea into something real. A prototype does not need to be built in code or made of expensive materials. It can be a hand-drawn sketch of how an app would work, a paper mockup of a form, a rough script for a conversation, or a physical object made from whatever materials you have. The point is to make the idea tangible enough that someone else can interact with it and give you feedback. Prototyping quickly and cheaply is a discipline: the goal is to learn as fast as possible, not to produce something polished. The polish comes later, after you know you have the right thing.