Prototypes are something you build to convince yourself. Demos are something you build to convince others.

You build a prototype to answer a question. What is the question your prototype answers? When you define this question, it shows you what you should build and what you should fake.

When prototyping, think of the cheapest way to answer your question. There is an even cheaper way to answer your question.

In industrial design, there are "looks-like" prototypes and "works-like" prototypes.

Building many small prototypes will always be easier than building one mega-prototype.

If you find yourself building One Prototype to Rule Them All, you are not building a prototype, you are building a product.

There is another kind of prototyping, which I call build to think. It is open-ended play with an eye toward discovery. When building to think, it's smart to define your timeframe and runway.

Every demo is built for an audience and a goal.